By kevinrutherford
via silkandspinach.net
Published: Jan 11 2008 / 10:43
Suppose you flip a coin 1000 times. Keep a cumulative sum, starting with zero: every time the coin comes up heads you add 1 to your running total; and every time it comes up tails you subtract 1. How many times will the cumulative sum equal zero? How many flips will there be, on average, between the times the sum equals zero?
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