A brown-eyed father and a green-eyed mother have a 25% chance of having a green-eyed child. What is the probability that, in a family of four children, three of them have green eyes?

Question

a. 0.421 875 c. 0.011 718 75 b. 0.046 875 d. 0.1875

Answer 1

If the child who doesn’t have green eyes is the youngest, then the probability is 0.25³×0.75=3/256.  But that child isn’t necessarily the youngest, so we need to multiply this probability by 4=0.046875, answer b.