The sample space is these 8 lines below.


1)    B B B 

2)    B B G

3)    B G B

4)    B G G


5)    G B B 

6)    G B G

7)    G G B

8)    G G G


Of these 8 lines,  lines  2), 3) and 5)  represent  "two boys in a family".

                   Lines  4), 6) and 7)  represent  "two girls in a family".


P(two boys in a family) = .


P(two girls in a family) = .