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Possum's Journal

26th February, 2004. 5:14 pm. un-squashing the trading graph

Betfair's 'trading graph' for each runner is a 350x225 pixel image, but the site tries to fit it into a 350x210 pixel space. This results in the image being a bit squashed, and losing some rows of pixels.

If you're a privoxy user, you can fix the problem by adding these lines to default.action:

# ------------------------------------------------------------------------
{+filter{betfair-chart-size}}
/Betting/MoreInformation.asp
# ------------------------------------------------------------------------

and these lines to default.filter:

# ------------------------------------------------------------------------
FILTER: betfair-chart-size
s!img name=chart width=350 height=210!img name=chart width=350 height=225!
# ------------------------------------------------------------------------

If you're not a privoxy user, you can find it at http://www.privoxy.org/

(9 messages | leave a message)

1st October, 2003. 12:00 pm. this is not the journal entry you're looking for

move along...

(1 message | leave a message)

13th August, 2003. 11:30 pm.

On Betfair, if you try to place a bet for odds of 100 or more you get a dialog box pop up telling you that the odds are over 99. This could be useful I suppose if you're laying and accidentally added a zero, but if you're attempting to back then surely the higher the odds the better. Anyway, I decided to turn the warning off.

Similarly, if you enter odds which aren't allowable, such as 11.1, then you'll see another dialog telling you that the odds aren't allowable. The odds you entered will then be rounded up or down depending on whether you're laying or backing respectively. I decided to turn that warning off too.

If you also want these warnings to stop bothering you, follow the following steps. What will happen is that the dialog will still appear, but a small program running in the background will automatically click 'OK' on the dialog to close it almost before you can see it.

  1. Download QuickMacros from http://www.quickmacros.com/, install it and run it. Make sure QuickMacros runs itself when windows boots. I think that's an installation option.

  2. On the 'file' menu choose 'new' -> 'new macro'.

  3. Rename the new macro if you like to some name you'll remember.

  4. Left click the new macro from the list on the left to select it.

  5. In the text area in the top right paste the following:
    if (child("Odds value is out of the acceptable range" "Static" val(command)) or \
    child("Warning: You have entered odds greater than 99." "Static" val(command)))
    but "OK" val(command)
    
    Note that that is should only be two lines. I have had to split the first line into 2 lines to fit it in this journal. You should join them together again, and remove the '\' from between them.

  6. Right click the new macro (in the list on the left) and choose 'properties'.

  7. Click 'created window'.

  8. Put 'Microsoft Internet Explorer' (without the quotes) in the 'Window name' box.

  9. Check 'it is a popup window'

  10. Check 'exact'

  11. Click 'OK'

  12. Click the floppy disk icon to save everything.
That should do it. Try backing some favourite at odds of 999 and see if the warning dialog appears and disappears quickly.

(1 message | leave a message)

12th August, 2003. 5:53 pm. Links

Microsoft's Fix for the Blaster Worm:
for Windows XP:
http://microsoft.com/downloads/details.aspx?FamilyID=2354406c-c5b6-44ac-9532-3de40f69c074&displaylang=en
for Windows 2000:
http://microsoft.com/downloads/details.aspx?FamilyID=c8b8a846-f541-4c15-8c9f-220354449117&displaylang=en

SANS:
The Twenty Most Critical Internet Security Vulnerabilities
http://www.sans.org/top20/

Microsoft:
How to Disable DCOM Support in Windows
http://support.microsoft.com/default.aspx?scid=kb;[LN];825750

EWeek:
Securing Windows
http://www.eweek.com/category2/0,3960,1122122,00.asp

TruSecure Corp:
Hype or Hot
http://www.trusecure.com/knowledge/hypeorhot/2003/tsa03011.shtml

Micro TechNet:
Microsoft Security Bulletin MS03-026:
Buffer Overrun In RPC Interface Could Allow Code Execution (823980)
http://www.microsoft.com/technet/security/bulletin/MS03-026.asp

The Register:
MSBlaster worm spreading rapidly
http://www.theregister.co.uk/content/56/32286.html

SANS:
RPC DCOM WORM (MSBLASTER)
http://isc.sans.org/diary.html?date=2003-08-11

CERT:
Steps for Recovering from a UNIX or NT System Compromise
http://www.cert.org/tech_tips/win-UNIX-system_compromise.html

LSD - the Last Stage of Delirium:
The Polish group which discovered the RPC buffer overrun security hole
http://lsd-pl.net/special.html

Xfocus:
The Chinese group which produced the first exploit of the RPC buffer overrun exploit
http://www.xfocus.org/

(leave a message)

11th August, 2003. 7:07 pm. Putting Newest Bets First When Ordering By Matched Date

When 'order by matched date is ticked the bets are sorted so that the bets which were matched first are listed first. It used to be the other way around, which I found more useful.

You can change this back to putting newest bets first using a proxy server to edit the code that www.betfair.com sends to your browser.

The steps are exactly the same as for fixing the 'bets-in-the-wrong-order' bug - just the two code snippets are different.

To reverse the sorting order:

Add this to the default actions:

# ------------------------------------------------------------------------
{+filter{betfair-reverse-sort}}
/7/1608/1649/1107/www.betfair.com/Betting/includes/BetMgr_SortFunc.js
# ------------------------------------------------------------------------
and add this to the filters:
# ------------------------------------------------------------------------
FILTER: betfair-reverse-sort
s!(\t*return sDate1>sDate2\?)1:!$1-1:!U
s!(\t*sDate1<sDate2\?)-1:0;!$1 1:0;!U
# ------------------------------------------------------------------------

(leave a message)

10th August, 2003. 5:48 am. Changing the Frequency of Automatic Updates

By default Internet Explorer waits for 30 seconds between each automatic refresh of the odds display on Betfair. The refresh itself can take a second or two resulting in a time-between-refreshes of 31 or 32 seconds.

You can change this waiting time to any amount you like using a proxy server to edit the code that www.betfair.com sends to your browser.

The steps are exactly the same as for fixing the 'bets-in-the-wrong-order' bug - just the two code snippets are different.

To change the delay between automatic refreshes:

Add this to the default actions:

# ------------------------------------------------------------------------
{+filter{betfair-refresh}}
/Betting/BetMgr_HTMLInterface.asp
# ------------------------------------------------------------------------
and add this to the filters:
# ------------------------------------------------------------------------
FILTER: betfair-refresh
s!var iRefreshInt=30000;!var iRefreshInt=20*1000;!U
# ------------------------------------------------------------------------
The line that says "s!var iRefreshInt=30000;!var iRefreshInt=20*1000;!U" is telling privoxy to replace the line of code that sets the refresh period. It is usually set to be 30000 milliseconds (30 seconds), and we are changing it to be 20*1000 milliseconds (20 seconds). If you want the refresh to be more or less regular then change the 20 to whatever delay you want it to be. If you make it too low, however, then it's possible that your browser won't be able to finish displaying the page properly before the timer goes off again and makes it start all over again.

(5 messages | leave a message)

31st July, 2003. 10:51 pm. Casinos in the UK

AB10 1SJ; Gala Casinos; 59, Summer St; Aberdeen Aberdeenshire; Tel: 01224 645273
AB15 4YL; International Casino; 9, Queens Rd; Aberdeen Aberdeenshire; Tel: 01224 208686
B1 2HF; Grosvenor Casinos; 263, Broad St; Birmingham West Midlands; Tel: 0121 631 3535
B5 4BN; Stanley China Palace Casino; 16, Hurst St; Birmingham West Midlands; Tel: 0121 622 3313
B62 9NU; Royale Casino Entertainments; 158, Summerfields Avenue; Halesowen West Midlands; Tel: 0121 422 5100
BH1 1DA; Stanley Bournemouth Casino; 9, Yelverton Rd; Bournemouth Dorset; Tel: 01202 293188
BN1 1PP; Grosvenor Casino; 9, Grand Junction Rd; Brighton East Sussex; Tel: 01273 326514
BN2 5UT; Rendezvous Casino; Brighton East Sussex; Tel: 01273 605602
BS1 6NL; Gala Casinos; Redcliffe Way; Bristol Avon; Tel: 0117 921 3189
BS9 2JX; Royale Casino Entertainments; 24, West Parade Sea Mills; Bristol Avon; Tel: 0117 923 6777
CF10 1AB; Les Croupiers; 32, St. Mary St; Cardiff South Glamorgan; Tel: 029 2038 2810
CF10 3AD; Grosvenor Casino; Greyfriars Rd; Cardiff South Glamorgan; Tel: 029 2034 2991
CF71 7NY; Royale Casino Entertainments; Brambles, Grove Rd Llandow; Cowbridge South Glamorgan; Tel: 01656 890162
CH7 3LG; Las Vegas Fun Casino; 2, Etna Rd; Buckley Clwyd; Tel: 01244 547102
DE1 1BU; Stanley Carlton Casino Club; 6, Friar Gate; Derby Derbyshire; Tel: 01332 368074
DE1 1LA; Stanley Grand Casino; 2, Colyear St; Derby Derbyshire; Tel: 01332 368880
EH1 3EB; Stanley Edinburgh Casino; 5b, York Place; Edinburgh Midlothian; Tel: 0131 624 2121
FY4 1BB; Grosvenor Casino; The Sandcastle, Promenade; Blackpool Lancashire; Tel: 01253 341222
G2 3LW; Gala Casinos; 528, Sauchiehall St; Glasgow Lanarkshire; Tel: 0141 332 8171
G2 6LL; Gala Casinos; 95, Hope St; Glasgow Lanarkshire; Tel: 0141 226 3856
LE1 4SU; Stanley Leicester Casino; 17-19, East Bond St; Leicester Leicestershire; Tel: 0116 262 5036
LE7 7BN; Royal Flush Fun Casinos; 186, Cropston Rd Anstey; Leicester Leicestershire; Tel: 0116 236 4481
LL11 2HL; Race Nights Casinos Promotions; Mountain View, New Rd; Wrexham Clwyd; Tel: 01978 312980
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LU1 1EE; Grosvenor Casino; Dunstable House 50, Dunstable Rd; Luton Bedfordshire; Tel: 01582 414166
M1 3; Cicus Casino; 110, Portland St; Manchester Lancashire; Tel: 0161 228 0077
M1 4HQ; Grosvenor Casino; 35-39, George St; Manchester Lancashire; Tel: 0161 236 7121
M3 1JA; Grosvenor Casino; 2, Empire St Cheetham Hill; Manchester Lancashire; Tel: 0161 834 8433
M4 2BS; Hard Rock Casino; The Print Works 27, Withy Grove; Manchester Lancashire; Tel: 0161 838 5300
M5 4SX; Grosvenor Casino; Riverside, Regent Rd; Salford Lancashire; Tel: 0161 839 0467
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NG1 6HS; Gala Casinos; 4, Maid Marian Way; Nottingham Nottinghamshire; Tel: 0115 979 9288
NR30 3JG; Grosvenor Casino; Marine Parade; Great Yarmouth Norfolk; Tel: 01493 850444
PL1 2SR; Stanley Grand Casino; 2, Union St; Plymouth Devon; Tel: 01752 228930
PO4 0SR; Grosvenor Casino; Savoy Court, South Parade; Southsea Hampshire; Tel: 023 9273 2277
PO5 3LT; Grosvenor Casino; 18, Osborne Rd; Southsea Hampshire; Tel: 023 9282 1512
PR9 0QG; Stanley Southport Casino; 180, Lord St; Southport Merseyside; Tel: 01704 537427
RG1 4SY; Grosvenor Casino; 1, Queens Rd; Reading Berkshire; Tel: 0118 959 4642
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SR5 1AD; Gala Casinos; North Bridge St; Sunderland Tyne and Wear; Tel: 0191 5145551
SS0 7QY; Westcliff Casino Ltd; Western Esplanade; Westcliff-On-Sea Essex; Tel: 01702 352919
ST1 4EU; Stanley Stoke Casino; 14-16, Broad St Hanley; Stoke-On-Trent Staffordshire; Tel: 01782 213499
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SW1X 7RQ; Park Tower Casino; 101, Knights Bridge; London; Tel: 020 7235 9595
SW7 4LJ; Grosvenor Casino; The Gloucester 4-18, Harrington Gardens; London; Tel: 020 7373 7134
SW8 1XX; Viva Vegas Casino Entertainments; 144a, Old South Lambeth Rd; London; Tel: 020 7820 0999
W1H 7AW; The Sportsman Casino; 40, Bryanston St; London; Tel: 020 7414 0061
W1J 7ED; Les Ambassadeurs Club; 5, Hamilton Place; London; Tel: 020 7495 5555
W1J 7TN; Crockfords Club; 30, Curzon St; London; Tel: 020 7493 7771
W1J 9ET; Gala Casinos; 196, Piccadilly; London; Tel: 020 7534 7600
W1K 1HD; The Rendezvous Casino; 14, Old Park Lane; London; Tel: 020 7491 8586
W1T 1PS; Allman; 2nd floor 29, Newman St; London; Tel: 020 7255 2515
W1U 6HL; Royale Casino Entertainment; 80, Gloucester Place; London; Tel: 020 7486 6755
W8 4RE; The Connoisseur Club; Royal Garden Hotel Kensington High St; London; Tel: 020 7603 1155
WC1B 5BA; Gala Casinos; 61-66, Russell Square; London; Tel: 020 7833 1881
WS2 0LE; Grosvenor Casino; 2, Bentley Mill Way; Walsall West Midlands; Tel: 01922 645222
WV1 1JR; Gala Casinos; Whitmore St; Wolverhampton West Midlands; Tel: 01902 423267

(leave a message)

28th July, 2003. 12:01 pm.

.------------------------------------------------------------------------
|  General Betting   :   Probability Quiz No.16 - Cont
'------------------------------------------------------------------------

Posted by : getting better 29 Jul 21:46

I have attempted to answer to this question this question myself and come to the following conclusions: 1. The question has some remaining ambiguities, which are not very material (I favour the 14 day, 14 night rule myself) 2. I come to a different answer to both Mac and Galejo 3. I am not sure my answer is right 4. But I am strongly inclined to think they are both wrong 5. The question is very tedious and has no neat solution 6. Can we withdraw the question to avoid further tedium please? All these questions are based on real life problems, and I usually don't knwo the answer. Sometimes like the ginger hunt they come out with nice solutions, sometimes like the snails they lead to genuine controversies. But occasionally they are vague and tedious. Let's just hope next week's proves more interesting! [Apaprently we are all "saddos" even the migthty possum!]

Posted by : Possum 30 Jul 00:58

'mighty'? huh?

Posted by : Mac 30 Jul 03:49

1. True 2. You don't say! 3. That's a relief 4. Why? 5. Disagree. Building a spreadsheet is just as neat/tedious as building a simulation. 6. Sure - you're the QuizMaster! (7. What about our points? There's a lot at stake here...) Bear in mind that (a) it sparked some good discussion (b) galejo and I came to the same answer - or would have if we used the same assumptions! I for one would be interested in why you are strongly inclined to think we are wrong...

Posted by : Jd777 30 Jul 08:14

agreed with 5 at a glance yesterday!!

Posted by : getting better 31 Jul 20:55

pssum where is the league please?

Posted by : Possum 31 Jul 22:33

gb - I didn't update it for a long time.

how are you going to award points for the 'missing' week?

(you know the url, don't you? if not, go to the FAQ, click 'memories' at the top of the page & you'll find it)

Posted by : Possum 31 Jul 22:33

what about this week? null point all around, or what?

Posted by : Mac 01 Aug 03:31

I protest! Given that I can duplicate galejo's answer - albeit with different starting assumptions - I reckon our approach is valid and we should share 1st and 2nd points (divide mine by two for my extra cherry bite).

A propos of nothing, the highlights of the MU-Juventus game provide a beautiful example of the sublime (van Nistleroy's goal) and the ridiculous (Forlan's astonishing miss). Not to be missed.

Posted by : getting better 01 Aug 20:35

Well we did award points for the missing week, but it was lsot. I think we should trust people to claim them, as there is no dispute about the result.

(leave a message)

28th July, 2003. 12:00 pm.

This is one of the questions from a series of probability questions set by a user called 'getting better' on the Betfair forum.

.------------------------------------------------------------------------
|  General Betting   :   Probability Quiz no.16 - Holidays and Operations
'------------------------------------------------------------------------

Posted by : getting better 28 Jul 12:00

I would like to book a holiday tomorrow (29th July 2003) but I don’t want to miss a minor eye operation I am waiting for at Moorfields Eye Hospital. They will write to me four weeks before the operation, the letter will arrive the next working day and I have to write back within a week (five working days) of the letter confirming the operation else it will be cancelled. I would like to book a two week holiday (starting any day of the week), and I will not leave until the post arrives on that day, but I will be back too late to reply on the day I return. I cannot have the operation on the day I leave, or the day I return (or whilst I am away obviously).

They may write to me any day, starting tomorrow 29th July 2003. Both the offices and the clinic are shut (except for emergencies) for Christmas from Thursday 25th December to Friday 2 January inclusive.

The letter could arrive any time from Wednesday 30th July onwards, but the expectation of the time I must wait for an appointment is 20 weeks (100 working days). The chance of the letter arriving each day (given that it has not already arrived) is 2% greater than it was the day before, as they give a slight priority to those who have been waiting longer.

I do not want to book a holiday if there is a greater then 10% chance of losing the operation due to the holiday. So for what start dates can I not book my holiday?

Posted by : galejo 28 Jul 12:08

Is the clinic open weekends or only Mon-Fri?

Posted by : galejo 28 Jul 12:13

"The chance of the letter arriving each day (given that it has not already arrived) is 2% greater than it was the day before"

As in 30%, 32%, 34% or 30%, 30.6%, 31.212% (both of which will exceed 100%) or as in some other way that would converge to 100%?

Posted by : getting better 28 Jul 12:20

It's only open Mon-Fri

If it's .05 one day, its .051 the next etc. Eventually it gets to 1 and you are right at the very top of the list.

Posted by : the parkie 28 Jul 12:29

Presumably it is not a sightseeing trip?

Posted by : Mac 28 Jul 12:34

"They may write to me any day, starting tomorrow 29th July 2003"

Meaning I may get the letter, or they may send it?

(Sense suggests the former; logic the latter.)

Posted by : getting better 28 Jul 12:37

No the first day they could write is tomorrow, and the first day I could get it is Wednesday. I've only just posted the form to them.

Posted by : Mac 28 Jul 12:37

RTQ; ignore.

Posted by : Possum 28 Jul 13:00

does the postal service work on Saturdays?

Posted by : getting better 28 Jul 13:23

Sometimes. For the question you can assume it does if it helps.

Posted by : galejo 28 Jul 13:25

Does this mean that the clinic do not send out any letters after 26th Nov or before 8th Dec?

If they do, then when do they send out the letter detailing an appointment on the 22nd Jan?

Posted by : eggshells 28 Jul 13:34

Will you be able to read the letter?

Posted by : getting better 28 Jul 13:51

I should think they'll still send the letters out 20 working days before the appointment, so for 22nd Jan they send on 16 December. But I really hope that it will be done before Christmas.

Posted by : galejo 28 Jul 13:58

Hmmm, in which case I just can't see that you have any worries booking a holiday at anytime. If the expectation is 100 working days from now that you get your appt then I make the 10th Dec the most likely day you'll get a letter but even then it is only around 0.87% that you receive the letter on that exact day. Even if you missed a whole 10 working days of letters, can't see them going over the 10% mark.

I must be missing something ...

Posted by : getting better 28 Jul 14:02

Maybe I'm worrying unduly but my fear is that I miss the operation either because the letter comes while I'm away or because the operation itself falls during the holiday.

Posted by : galejo 28 Jul 14:07

Ah yes - I knew I was missing something obvious - cheers ...

Posted by : galejo 28 Jul 14:35

OK I'd avoid booking holidays that start in any of the following periods (all dates are inclusive):

30 Sep - 3 Oct 6 Oct - 10 Oct 13 Oct - 17 Dec 1 Jan - 6 Feb 9 Feb - 12 Feb

A holiday that starts on any other day should be fine.

Posted by : Mac 28 Jul 14:37

I have an answer, but there is some ambiguity here:

They will write to me four weeks before the operation

The chance of the letter arriving each day (given that it has not already arrived) is 2% greater than it was the day before

If it's four weeks, they won't write 4 weeks before the Christmas period - but the probability should increase.

Should we assume they will write 20 working days before, or that the probability does not increase over that 4-weeks-till-Christmas period?

Posted by : getting better 28 Jul 14:47

mac -see my answer to galejo's qeustion -doers that help?

Posted by : alb in spirit 28 Jul 14:51

just phone them up and tell them the dates of your holiday , and they will switch your appointment if it is due on or between them dates with someone who is behind u on the waiting list , phone up the hospital concerned and ask for 1st appointments , they will tell u when u are expected for the op by appointment dates they have , they only ask u for availability just incase there is a cancelled appointment date , alb

Posted by : Mac 28 Jul 15:27

Don't start a holiday in the following periods (all dates inclusive):

29-Jul 13-Aug to 26-Aug 19-Oct to 20-Oct 23-Oct to 27-Dec 31-Dec to 20-Jan

Posted by : the parkie 28 Jul 15:28

Have you taken the August bank holiday and national no swearing week into account?

Posted by : getting better 28 Jul 15:31

I assume they work the august bank holdiay and get paid double time. Why does the no swearing week affect it?

Posted by : galejo 28 Jul 15:56

Mac - what day do you make the most likely to have the operation and what chance do you give it - I make it 6th Jan at a chance of slightly less than 0.87% ...

Posted by : Mac 28 Jul 16:16

Hi galejo - I have 13.16% on Tuesday 26th August

Posted by : galejo 28 Jul 16:23

Mac, now you've lost me. 26th Aug is the first day the operation could take place and I only make it around a 0.345% that the operation will happen on that day - why the far greater chance?

Posted by : Mac 28 Jul 16:43

My approach may be cock-eyed, but here goes.

First day op could be is x% Thereafter cumulative chance increases --> x*1.02 etc until =1 Subtract to get chances on specific days Set x to satisfy condition that expected no of working days till op = 100

Posted by : galejo 28 Jul 16:52

Slightly different for me, I took the 1.02 factor to affect conditional not cumulative probs. Then worked out cumulative and individual probs from conditional ones.

Then solved for 100 expectation as you mention.

Reckon the rest of the workings are probably the same though ...

Posted by : Mac 28 Jul 17:31

Hmmm... that makes a difference. Somehow I seem to have skipped that bit Still don't agree - 0.354% yes, but just over 0.874% for most likely, on 5th Jan. Not much difference there, but I may have made a cock-up in my date calculations as I'm still way out on those even with the different input probs.

Time for reflection...

Posted by : Mac 28 Jul 17:49

Don't start holiday on any of these dates (inclusive): Oct 19-20 Oct 24 - Dec 15 Jan 2-29 Feb 1-2

Posted by : parryhandy 28 Jul 18:53

dont tell them when your holiday is because one of the waiting list figure cheats was to find out when patients were on holiday then book them in for them days, you cancell and that counts as another person having been dealt with for their figures.remember reading this somewhere....

Posted by : galejo 28 Jul 20:56

Mac, you're taking the 1st operation day (26th Aug) to be in 20 working days time yep, so the expectation is 100 working days which would be an operation day of 16th Dec (letter sent 18th Nov) - do these figures tally?

Posted by : Mac 28 Jul 21:25

Mac, you're taking the 1st operation day (26th Aug) to be in 20 working days time yep, so the expectation is 100 working days which would be an operation day of 16th Dec (letter sent 18th Nov) - do these figures tally?

I agree operation day of 16th Dec has letter sent 18th Nov, sure - but is it relevant that this is in 100 working days time? Actually, I think I have Dec 16th as being in 101 working days, from today that is...

Not sure why the substantial disagreement - any ideas?

Posted by : galejo 29 Jul 08:01

We only have a small difference on the first part don't we 0.345% as opposed to 0.354%, this is purely down to the 1 day difference mentioned.

Why the big differences after that I'm not sure - will post some further figures later to try and nail it down.

Posted by : galejo 29 Jul 10:53

Mac, on the next part of the question, to work out the prob that going on holiday on 30th Sep (for example) will make me miss the operation then I've said that I will not be able to respond to any letter in time that has been posted between 30th Sep and 7th Oct (5 working days before end of holiday) and I will miss any operation in between 30th Sep and 14th Oct.

Using my dates (I know they're 1 out from yours, but the results should be fairly similar), I get 4.04% (chance I miss the letter) plus 5.97% (chance I'm away for the op) = 10.01%.

You similar?

Posted by : getting better 29 Jul 12:54

I wish someone like Possum or JD777 would confirm the answer. I'm not sure what I've done to offend them but they are posting all over the forum but boycotting the quizzes. Very worried especially about Possum as he is the official scorer.

Posted by : Possum 29 Jul 14:10

don't worry about me - I was really wasn't in the mood for a probability quiz yesterday. both the PC and the horses were playing up and I didn't need any extra distraction.

I read it through but didn't really know how to begin tackling it, so I threw in the towel.

I'll take a look now and see what I think...

Posted by : getting better 29 Jul 14:14

welcome back. Don't worry if you're busy - I'll leave it open until tomorrow for you. Hope the scores and thraeads are safe are safe.

Posted by : Jd777 29 Jul 14:24

wasn't online yesterday and looked a bit too much like hard work this one - but I'll take a look tomorrow morning

Posted by : Mac 29 Jul 14:41

Right - back at the trough. Morningal.

If I go on holiday on Tuesday 30th Sep, my impression is that I will be back in time for an operation on 14th Oct as I will be back on the 13th. So chance I'm away for the op = 5.52%

I figure I will miss any letter posted between 30th Sep and 5th Oct. If a letter is sent on Monday 6th, I get it on Tuesday 7th. I will be back on Monday 13th and able to reply on Tuesday 14th, which is within 5 working days (W-Th-Fr-Mo-Tu) of receiving it. My interpretation, anyway. So chance I miss out because of getting the letter in an unreplyable period = 2.72%

Looks like you have more bad dates than I do because you have two more letter days and one more holiday day. I shall post and re²-read the question...

Posted by : galejo 29 Jul 14:53

OK, think we've found most (if not all) of the differences:

1. I've taken the expectation of 100 days from 29th July, you've taken it from 28th July. 2. If I go on holiday on 30th Sep, surely I get back on the 14th Oct not 13th Oct? 3. 5 day limit for replying to letter I took from it being sent, not me receiving it (mainly because it was going to be sent on a business day, whereas I could receive it on a non-business day).

Think that should account for most of it ...

Posted by : Mac 29 Jul 15:02

"Think that should account for most of it ..."

Yes - now we can argue about the details... I think we have the big picture! (1) The original problem was set on 28th July, hence that was my start point (2) Er... a two week holiday lasts 14 days, surely? (3) "I have to reply within 5 days" - reasonable to assume from receiving it. If I get it on a Saturday, I should be OK if I reply by Friday at latest, no?

Posted by : galejo 29 Jul 15:11

(1) Maybe, still think it's a bit ambiguous though. I took it that the expectation would be from the time the clinic received the application (tomorrow) rather than when I sent it. Not gonna argue too strongly though.

(2) Pretty sure on this one though, yep it's a 14 day holiday say Sat through Sat, it mentions in the question (I think) that the operation cannot be had on either day, that's 15 days out in total. If I leave on 30th Sep after the post has been received, I'm definitely returning on 14th Oct aren't I?

(3) Once again, not gonna argue too strongly on this one, but I took it that they'd give you 5 days from them sending it. Could be taken either way.

Posted by : Mac 29 Jul 15:34

Guess we need arbitration :) I'm prepared to argue (2) - I don't think the question gives an example, just says a two-week holiday. If I leave on a Wednesday (and I can't have the op that day) surely a two-week = 14-day holiday will finish on a Tuesday?

Or is this the kind of woolly-minded liberal thinking that gets you eaten?!

Time for gb to wield the arbitration stick... I think we both have the correct answer given clarification on the parameters!

Posted by : Possum 29 Jul 15:49

if you book a 2 week holiday then you'll generally arrive back at the airport about 2 hours before the 14 days is up - to give them a chance to clean the plane and get the next bunch of holidaymakers on it.

So if you leave at noon on Wednesday 1st you can expect to be back at 10am on Wednesday 15th.

Two weeks surely have 14 days and 14 nights (even if one of those days is split into 2 half days)

Posted by : galejo 29 Jul 16:01

Agreed with you Possum, but in the question gb clearly says that the operation cannot take place on the day that he leaves or the day he returns - that's 15 days surely init?

Posted by : Mac 29 Jul 16:13

Yes - if you go on a Wednesday and return on a Wednesday. But that's a quinzaine in French parlance, or a little over two weeks in my book! And you would need to book 11 days > 2 weeks off work...

Posted by : galejo 29 Jul 16:23

Yep - agreed, you'd need to book the extra day off!

However, that is what gb says in the question isn't it. Reading it, he definitely says that if you leave on a Monday you're gonna miss 11 possible operation days - Mon thru Fri, Mon thru Fri and also the Mon you return.

Please tell me I'm not going mad!

Posted by : Jd777 29 Jul 16:23

the problem is that most people talk about a number of nights on holiday to avoid this ambiguity

Posted by : Jd777 29 Jul 16:25

but in my book a three-day holiday is the same as a two-night holiday (unless you're flying a long way overnight!)

Posted by : getting better 29 Jul 18:08

Sorry about the ambiguities The trouble is that because these questions are original and based on reality, they do not always translate exactly into clear logical problems I'll clear up these issues very soon

Posted by : Possum 29 Jul 19:21

he doesn't say where he means 14 nights or 13 nights. but since he says "a two week holiday" I think we have to assume that he means 2*7*24 hours, or there abouts. That's what two weeks means after all.

(leave a message)

22nd July, 2003. 12:00 pm.

This is one of the questions from a series of probability questions set by a user called 'getting better' on the Betfair forum.

.------------------------------------------------------------------------
|  General Betting   :   Probability Quiz No. 15 - Ginger Hunt
'------------------------------------------------------------------------

Posted by : getting better 22 Jul 13:23

My mother needs your help to working out probability of being able to buy some crystallized ginger to make a cake. It is very hard to get in the local town; sometimes this is because the crop has failed, and there is none available anywhere, but usually it is because of the unpredictability of the stock control systems of the local shops, which operate independently of each other.

The best chance is Tesco, where the probability of being able to buy ginger is the same as that of the crop having failed. The least likely is Somerfield, where there is only half the chance as at Tesco.

The probability that at least one of the shops on this side of town, Asda or Somerfield, has the ginger is the same as that of Tesco having it.

If the crop hasn’t failed, then there is a one third chance of being able to buy ginger on the other side of the town, where Tesco and Waitrose are based.

If the sum of the probabilities of being able to buy ginger at each of the 4 shops is 0.7125, what is the chance of being able to buy crystallized ginger somewhere in town?

Posted by : Jd777 22 Jul 13:28

hate to say it but still getting no solution gb

Posted by : galejo 22 Jul 14:14

Agree with JD, Waitrose comes out as -4.65% I think.

Posted by : BotMan 22 Jul 14:20

agreed, Waitrose negative

Posted by : Possum 22 Jul 14:50

> The best chance is Tesco, where the probability of being able to buy > ginger is the same as that of the crop having failed.

Is that really what you mean? Not "of the crop having succeeded"?

Posted by : getting better 22 Jul 15:00

just back from lunch, I'll have a look

Posted by : getting better 22 Jul 15:26

My mother needs your help to working out probability of being able to buy some crystallized ginger to make a cake. It is very hard to get in the local town; sometimes this is because the crop has failed, and there is none available anywhere, but usually it is because of the unpredictability of the stock control systems of the local shops, which operate independently of each other.

The best chance is Tesco, where the probability of being able to buy ginger is the same as that of the crop having failed. The least likely is Somerfield, where there is only half the chance as at Tesco.

The probability that at least one of the shops on this side of town, Asda or Somerfield, has the ginger is the same as that of Tesco having it.

If the crop hasn’t failed, then there is an evens chance of being able to buy ginger on the other side of the town, where Tesco and Waitrose are based.

If the sum of the probabilities of being able to buy ginger at each of the 4 shops is 0.7125, what is the chance of being able to buy crystallized ginger somewhere in town?

Posted by : getting better 22 Jul 15:26

The original question was OK, JDS confused me

Posted by : BotMan 22 Jul 15:29

41.667% or 5/12

Posted by : galejo 22 Jul 15:31

Well Tesco is no longer the best chance, but:

Prob of crop not failing = 85.38% Prob of buying anywhere given crop hasn't failed = 57.31%

or Prob of buying anywhere full stop is 85.38% * 57.31% = 48.93%

Posted by : galejo 22 Jul 15:33

Gave two answers 'cause I wasn't sure whether you wanted prob of buying anywhere given crop hasn't failed or without knowing whether crop had failed or not.

Posted by : Jd777 22 Jul 15:49

hmm sorry about that gb, I will recheck!

Posted by : Jd777 22 Jul 16:06

Sorry gb, here were my workings tho - pehaps someone can spot my mistake let x be the prob of crop failure and t,s,w,a be probs of supermarkets having stock t=x and s = x/2 Prob(A or S) = t, so a + s - as = t, and so a(1-x/2) = x/2 and so a = x/(2-x) Prob(T or W | F') = 0.5. , Prob(T or W | F') = Prob ((T or W) and F')/Prob(F') and as the supermarkets can only be stocked when the crop hasn't failed Prob ((T or W) and F') = Prob(T or W).

so t + w - tw = 0.5(1-f) so w(1-x) = 0.5(1-x) - x so w = (1-3x) / 2(1-x)

hence my equation from b4: 3x/2 + (1-3x)/2(1-x) + x/(2-x) = 0.7125, which has no solution x in [0,1]

Posted by : Mac 22 Jul 16:13

After all that... 50% exactly!

Posted by : Mac 22 Jul 16:15

Jd:

Prob(A or S) = t, so a + s - as = t, and so a(1-x/2) = x/2 and so a = x/(2-x)

A and S are not independent...

Posted by : Jd777 22 Jul 16:16

it says they are in the question

Posted by : BotMan 22 Jul 16:21

Jd: you have to consider the cases of crop failing and crop succeeding separately when combining probabilities of two shops: e.g. if crop succeeds a(1-x)+s(1-x)-a(1-x)s(1-x)=t(1-x)

Posted by : albatross 22 Jul 16:22

51.49%

Posted by : galejo 22 Jul 16:32

Reading it again, there's a lot of ambiguity about the conditional parts to this question.

1. The prob that Tesco has stock is the same as that of the crop failing. This has to refer to the conditional prob that Tesco has stock given that the crop has not failed, otherwise the 50% chance of there being stock at Tesco or Waitrose given the crop has not failed is clearly wrong (it would be 100%).

2. If the Tesco probability from above is conditional then presumably the Safeway (half of Tesco) is also conditional.

3. The Waitrose or Tesco probability of 50% is clearly stated as conditional, but the big question is, is the Asda or Safeway probability (equal to Tesco) also conditional - I took it to be so as all the others were also and as a further step also took the sum of the 4 shops quoted (equal to 71.25%) to also be conditional of the crop having failed.

I think some clarification on the conditional parts could be needed ...

Posted by : galejo 22 Jul 16:38

Scrap that - sounds rubbish reading it back.

Posted by : Jd777 22 Jul 16:39

Can't agree Gal.

The question as stated implies that none of the probabilities are conditional other than the one that is explicitly stated as so

Posted by : BotMan 22 Jul 16:44

"If the crop hasn't failed" is written as applying only to the Tesco/Waitrose statement. I've taken all the other statements as unconditional.

Posted by : galejo 22 Jul 16:46

You're right jd - if none of them are conditional save the one stated then Waitrose remains -ve (-4.58% I think).

Only way I could solve it was assuming the conditional bit, but there is no reason to assume that as you state.

Posted by : getting better 22 Jul 17:04

As JD says none of the probabilties are conditional except where stated, but I really can't see why there isn't a positive solution (there may be negaitve or non-real solutions as well but my mother won't like them!)

Posted by : getting better 22 Jul 17:17

but read the probability of two stores being out of stock due to a crop failure is not indepenent of cOurse!

Posted by : BotMan 22 Jul 17:23

confirms 5/12 and if crop doesn't fail stock probabilities are 1/3, 1/4, 1/5, 1/6

Posted by : getting better 22 Jul 17:32

Possum in response to the orignial question thta is indeed what I mean sorry about the delay confirming that. There seem to be two camps forming, those who belvie the questionn has an answer and those who don't!

Posted by : BotMan 22 Jul 17:39

oops not 5/12, 50%, Mac is right, answer is 1-(1/4 + (1/3)*(3/4)) forgot the 3/4!

Posted by : Jd777 22 Jul 17:41

BotMan - I agree with what you have said in principle, but still get negative answers.

let x be Pr(failure) and t,s,a,w be probs CONDITIONAL on crop success. These are now independent.

t(1-x) = x ie. t = x/(1-x) and also s = x/2(1-x)

Prob (asda or sains have stock) = (1-x)(a + s -as) = t(1-x), so a + s -as = t Prob (tesco or wait have stock given success) = t + w - tw = 0.5 Sum of probs = (1-x)(t+s+a+w) = 0.7125

I still get a negative for waitrose

Posted by : Jd777 22 Jul 17:50

guess that puts me in agreement with gal ie get waitrose solving to -4.6% roughly

Posted by : BotMan 22 Jul 18:00

Sorry Jd, I think my algebra was a bit scrambled in my earlier reply

If c is probability of a crop and (1-c) of failure If there is a crop, stocking probabilites are t, s, a, w So overall probabilities are ct, cs, ca, cw

then ct=1-c s=t/2 a+s-as=t t+w-tw=1/2 ct+cs+ca+cw=0.7125

solve by substitution or by putting in an arbitrary value for c and adjusting it until the last statement agrees

then probability of success is 1-((1-c)+c(1-t)(1-s)(1-a)(1-s)) and the answer is 0.5

it's Somerfield, by the way, gb's mother never goes to Sainsbury's

Posted by : Mac 22 Jul 19:06

Probability of crop failure is 1/4, if that helps with calculations etc

Posted by : Jd777 22 Jul 20:13

ok I agree now - 50%

my algebra is fine but my numerical method must have converged on an improper root of the equation!

Posted by : Mac 22 Jul 20:42

Yes - there is a solution where the Tesco, Waitrose, Somerfield and Asda probs are 0.34761, -0.04584, 0.173805 and 0.236925 respectively. Interestingly if you ignore the negative figure and just calculate the answer you still get 50%

Posted by : Jd777 22 Jul 21:27

hmm suggests that there's a shortcut without all this algebra...

Posted by : Possum 23 Jul 01:29

solving the cubic equation 520c^3 - 858c^2 + 435c - 63 = 0 gives three different possible values for c:

c = 0.247610434 leads to t, s, a, w = 0.752389566 0.376194783 -0.724425289 0.308340884 c = 0.652389575 leads to t, s, a, w = 0.347610425 0.173805213 0.236925227 -0.045840862 c = 0.750000000 leads to t, s, a, w = 0.250000002 0.125000001 0.150000001 0.187499997

all 3 solutions lead to a final answer of 0.50. odd, isn't it?

Anyway, that's my answer - 0.50.

Posted by : getting better 23 Jul 09:06

In jd's notation: Answer= c- c(1-a).(1-s).(1-w).(1-t) =c-c(1-t).(1-.5) =c/2+ct/2 =c/2+(1-c)/2 =0.5

Posted by : Jd777 23 Jul 09:21

like it gb

Posted by : Possum 23 Jul 11:22

how terribly clever!

gb - you often give the impression of not knowing the answer when you set these questions, so how come they work out so nicely?

this time, for instance, you weren't even sure that there WAS an answer, and yet you still end up with a cute little solution.

it's a kind of magic!

Posted by : BotMan 23 Jul 11:53

agree with Possum - a real beauty - looked like an ugly bastard, I mean .7125 - I ask you, then it falls out to really simple numbers: brilliant!

Posted by : Mac 23 Jul 12:43

Very nice Not clear how you go from c- c(1-a).(1-s).(1-w).(1-t) to c - c(1-t)(1-0.5) and/or how you use the 0.7125 but very nice all the same.

Posted by : getting better 23 Jul 12:54

In the question it says that:(1-a)(1-s)=(1-t) as this is the chance of not being able to get ginger on this side of the town, and the chance of not being able to get it at Tesco. It also says that if the crop has not failed there is a 0.5 chance of getting it on the far side of town, i.e. (1-w)(1-t)=0.5. You don't need the 0.7125 to get the answer, but the extra information actually makes the question harder because it distracts you from the simpler routes to the answer!.

Posted by : Mac 23 Jul 13:12

Quite delightful - hats off to you gb!

Posted by : getting better 24 Jul 06:43

Well done mac - 10 points

I think the others should be botman 3, jd777 2 and possum 3 (botman and jd777 both wrong on first answers)

Thanks for the kind comments, I'll try to keep them coming

Actually there may already be one on the pipeline as my colleague with the kids who went to chitty chitty bang bang has entered his children for a tennis competition which has some very complicated handicapping rules, but he is re-checking with organisers what the exact rules are.

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