Here, let B = child is male;
G = child is female.
The sample space of selecting one family from the families having
two children is expressed as follows:
U = {(B, B), (B, G), (G, B), (G, G)}
(1) Event A1 = One child is a female
= {(B, G), (G, B)}
(2) Event A2 = At least one child is a female
= {(B, G), (G, B), (G, G)}