Twenty fair tosses

Topic: Random variables and distributions · more questions on this topic
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A fair coin is tossed 20 times.

1. Find the probability of exactly 10 heads.

2. Find the probability of 15 or more heads.

Worked answer (click to show)

The number of heads is \operatorname{Bin}(20,1/2).

1. \binom{20}{10}/2^{20}\approx 0.176.

2. \sum_{k=15}^{20}\binom{20}{k}/2^{20}\approx 0.0207.