Blog: Plutonium

Posted by Plutonium on 18th July 2012 at 19:12 (3892 Views)
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JUL
18
2012
The three card trick
5 Comments
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One of the most fascinating, and controversial, areas of Maths is probability. Many people have mistaken ideas about 'odds', which of course suits bookies, casinos and others down to the ground.

Here's an example. A fairground entertainer has three cards in a hat. One is red on both sides, one is blue on both sides, one is red on one side, and blue on the other.

You take a card out of the hat and lay it on the table. The visible side is red. The entertainer bets you 10 that the other side is red, also.

Is that a fair bet?
Updated 18th July 2012 at 20:11 by Plutonium
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  1. Scrotnig -
    JUL
    18
    2012
    Scrotnig's Avatar
    It sounds like it. I am no mathematician but I reckon the odds will be very much in the entertainer's favour.

    Nick might know this one, he's a betting man....
  2. Evil -
    JUL
    19
    2012
    Evil's Avatar
    Seems like it's 50/50. Either it's the red/red card or the red/blue card.
  3. Memnoch -
    JUL
    19
    2012
    Memnoch's Avatar
    Evil
    Seems like it's 50/50. Either it's the red/red card or the red/blue card.
    Probability is often counterintuitive and this is an example of that.

    You have to analyse what you already know as well as what might happen next.

    You're looking at a red face. There are 3 ways that can happen:
    1. Side A of the red/red card
    2. Side B of the red/red card
    3. The red side of the red/blue card

    So, three possibilities of what you're actually looking at, and in two of those cases there's a red on the other side, so the game is 2-1 in the hustler's favour.

    Updated 19th July 2012 at 04:26 by Memnoch
  4. Evil -
    JUL
    19
    2012
    Evil's Avatar
    Ahhh. Very tricky.
  5. Plutonium -
    JUL
    20
    2012
    Plutonium's Avatar
    Memnoch is right.

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