The probability that one child is a girl is 1/2, then the probability for both children to be girls is 1/2*1/2 = 1/4
(a) Answer: 1/4
The probability that at least one child is a girl is 1-P(b) where P(b) is the probability that both children are boys. P(b)=1/2*1/2=1/4
(b) Answer: 3/4
The probability that both children are the same gender is the sum of the probability of both being girls (1/4) plus the probability of both being boys (1/4).
(c) Answer: 1/2