Total numbers of elementary events are: 2×2×2 = 8

(Each child could be either a girl or a boy)

Let E be the event of having at least one boy

(Note- at least one boy means there could be one or two or three boys in the family. The possibility of all the three girls is not considerable.)

P (having all girls) = P (not E) = 1/8

P (HAVING at least one boy) = 1- P (not E) = 1- 1/8 = 7/8