OT - Calc of Avg temperature

[whisky-dave]

And it can't be negative if you're measuring in the Kelvin scale :)

[Robin]

To be pedantic, subject to context: it used to be standard to use negative absolute temperatures when dealing with some aspects of stellar atmospheres to express population inversions :))

[djc]

And, according to some research, counter productive. The 'real world' context is meant to make the thing more 'accessible' to those less academically gifted. But those in the know, know it's just a homework question and all the real world clutter is to be stripped out first. Meanwhile the less academic, think in real world terms and are confused by all the half-baked context.

[John Rumm]

or sometimes the real world context can be a trick to misdirect you...

Like the question from a couple of months ago about a chap taking socks from the drawer in the dark. There are 15 brown ones and 6 black ones - how many does he need to take out to be sure he has a matching pair?

(the quantity of each colour is a misdirection leading one to think in terms of probabilities, skipping over the obvious answer)

[Tim Watts]

On Tuesday 04 February 2014 02:14 John Rumm wrote in uk.d-i-y:

Is he allowed to look at what he's taking out?

[The Medway Handyman]

If he is only allowed to look at what he has 'taken' out it doesn't make any difference. The answer is 3. Obviously if he is allowed to look at what he is 'taking' out its 2.

The 15/6 reminds me of the Six Card Swindle bar bet.

[John Rumm]

Yes, but its dark so he can't see...

[John Rumm]

Which one is that?

[Tim Watts]

On Tuesday 04 February 2014 16:01 John Rumm wrote in uk.d-i-y:

Ah - and yes, I get it now I've read it again...

[dennis]

Well the answer could be 20 as there is more to matching pairs of socks than the colour. There could be 13 different pairs and still match the colour specification. There could be no matching pairs and why one odd sock?

[The Medway Handyman]

Great bar bet.

Two red picture cards & four black spot cards are removed from a deck.

The cards are mixed face down & the mug punter is allowed to turn any two over. If both are black spots, he wins. If one or both are red pictures, you win.

You don't turn over the cards, only the punter does.

You explain that, since there are 4 black spots & only 2 red pictures, the odds are 2-1 in his favour - but since you are such a nice chap, you will play even money.

So, both put £1 into the pot, punter turns over two cards, if both are black spots he takes the pot, if not you do.

Very important to play as a freeze out bet e.g. you both start with 10 x £1 coins & continue to play until one of you is skint (the punter).

[The Medway Handyman]

Pillock.

[Tim Streater]

Whereas the actual odds of him picking 2 black spots are:

first card: odds 4/6

second card: odds 3/5

Overall odds for the pair (multiply because he has to win twice in a row in order to collect): 4/6 x 3/5 = 0.4

Conversely, your odds are:

first card: odds 2/6

second card: odds 2/5

Your overall odds (add because you get two goes to defeat him): 2/6 +

2/5 = 0.73

Hmmm, shome mishtake Shirley it ought to be 0.6.

[The Medway Handyman]

AIUI there are 15 possible combinations, 9 of which will contain a red picture.

[Tim Watts]

On Tuesday 04 February 2014 18:41 The Medway Handyman wrote in uk.d-i-y:

I found an old style "mechanical horse race" game down at one of the Brighton arcades.

20 mins of observation indicated that the probablility of each horse colour winning coupled with the gambling payoff was such that I could game the machine trivially.

I did and it worked,

However, at a return of 2p profit every few minutes I got bored after half an hour...

[Tim Streater]

I would have said 30 because there are 6 ways to pick the first card, and 5 ways to pick the second.

I just wrote it out longhand and of the 30 ways, 12 are good for the mark and 18 for the shark. Which implies that *all* my previous analysis was wrong -

Back to the drawing board.

[The Natural Philosopher]

Its the only way to do it simply I think.

[The Medway Handyman]

Unsure of the math - but it works, I've done it many, many times.

[John Rumm]

ISTR the original question specified they were the same apart from colour.

Are you going to tell me that you never have an odd sock in the drawer? ;-)

[Tim Streater]

Oh I agree that the real odds are 2 to 3 (in the shark's favour, IOW) rather than 2 to 1 in the mark's favour. But I ought to be able to work it out from first principles rather than the brute force approach, and I'm failing miserably.