Question

Find the probability that when a couple has fourfour ​children, at least one of them is a girlgirl. ​(assume that boys and girls are equally​ likely.)

Answer 1

A - at leats one is a girl

B - none is a girl

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Answer 2

This is a case of binomial probability, with n=4 and p=0.5.

Note that P(at least one of the four children is a girl) = 1 - P(no girls among 4 children).

P(no girls among 4 children) = binompdf(4,0.5,0) = 0.0625

Then P(at least one of the four children is a girl) = 1 - 0.0625 = 0.94.