Question 1163614
1--4--6--4--1
2 boys and 2 girls is 6/16 or 0.375 probability
no boys is 1/16 or 0.0625 probability
at least one boy is born is the complement or 0.9375 probability 
given at least 1 boy, probability of two boys
this would be 6/15, since given at least one boy decreases denominator from 16 to 15.
P(B|C) is 0.
A and C are not mutually exclusive, B and C are mutually exclusive

P(A)*P(C)= P(A and C)
(5/16)(15/16)=75/256; P(A and C) =P(A)=5/16
They aren't equal so are dependent.
Once you know 2 boys and 2 girls, you know there is at least one boy.