## Wednesday, October 19, 2005

### Don't you hate it when the machine won't take your money!

A long, metal slide resembling a sliding board has been constructed with 3 holes spaced out along the length of the slide. Coins are placed at the top of the slide and released one after another. For each coin that approaches the first hole the chances are 50 percent that it will fall through the hole. If it makes it past the first hole the chances are 50 percent that it will fall through the second hole. The third hole has the same chances.

How many coins need to be released so that chances are that one coin will make it all the way down the slide?

1. 8 it is.

The answer is based on probability theory. This problem is the same as calculating the probability of flipping a coin three times and getting heads all three times. The answer is 1/8.

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