**Annotation category:**

Chapter 4

Note: |

You might at first think if I flip a coin 100 times there are only ten chances to get 10 heads in a row. But there are really 91:

1 2 3 4 5 6 7 8 9 10, or

2 3 4 5 6 7 8 9 10 11, or

91 92 93 94 95 96 97 98 99 100.

Thus, if the chance of 10 heads is ~ 1 in 1,000 and I make 91 attempts, the odds are 1/1000 x 100 = 1/10 = 10%. See Chapter 5 for the precise definition of coin-flip probabilities.