Afair coin is flipped four times. what is the probability of getting heads at least once?

The probability of getting zero heads in four flips is (1/2)^4 = 1/16.
Therefore the probability of getting heads at least once in 4 flips is:                       1 - 1/16 = 15/16.

We have to find the probability of the opposite event and subtract that value from 1.

The opposite event would be getting zero heads (so all tails) .
P()=(1/2)^4 = 1/16
Hence,
1-(1/16)= 16/16 - 1/16 = 1/15

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20 percentage, you can also do it on a calculator.