Need an explanation please help clarify my confusion A paral

Need an explanation please help clarify my confusion...

A parallel situation would be observed were you to study families consisting of three children. If you were to select randomly 160 families each of which had 3 children:
a) in how many with the three children in the expected to be all boys?
b) two boys and a girl?
c) one boy and two girls?
d) three girls?

Solution

a) P(all three boys) = P(B) * P(B) * P(B) = 1/2 * 1/2 * 1/2 = 1/8

E(X) = Number of Evenents * P(all three boys)

=> 160 * 1/8 = 20

b) P(two boys and one girl) = P(BBG + BGB + GBB) = 3 * 1/2 * 1/2 * 1/2 = 3/8

E(X) = Number of Evenents * P(two boys and one girl)

=> 160 * 3/8 = 60

c) P(two girls and one boy) = P(BGG + GGB + GBG) = 3 * 1/2 * 1/2 * 1/2 = 3/8

E(X) = Number of Evenents * P(two girls and one boy)

=> 160 * 3/8 = 60

D) P(all three girls) = P(G) * P(G) * P(G) = 1/2 * 1/2 * 1/2 = 1/8

E(X) = Number of Evenents * P(all three girls)

=> 160 * 1/8 = 20