Tag Archives: math

Child Gender Ratios

There’s a country where everybody wants to have a son. Therefore each couple keeps having children until they have a boy; then they stop. What fraction of the population is female? (You may assume the question is asked as an expectation of course, since any particular country can be anything in principle — 100% girls […]

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Japanese Long Multiplication

This YouTube video makes it pretty clear how to do it; but I thought I’d run one without the graphical aids… 593 x 472 The trick is to arrange the nine necessary sub-multiplications in a standardised pattern. You can think of this as a square matrix rotated through 45 degrees… c 5|a b c b […]

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Chicken Prisoners

The Prisoner’s Dilemma is a well-known example from game theory. The basic idea is: Two men are arrested as being involved in the same crime. The police offer both the same deal: testify against your partner and you will go free and your partner goes down for twelve years. If you both remain silent, you […]

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