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Probability of at least 1 head =[5C1 + 5C2 +5C3 + 5C4 + 5C5] =31 / 2^5 =31 / 32

A fair coin is tossed five times.  What is the probability that heads appears at least once?

First find the probability heads doesn't appear at all:  p_{no_heads} = (1/2)⁵. 

So:   p_{at_least_one_head} = 1 - p_{no_heads}