Question

what's the probability of randomly meeting a four child family with either exactly one or exactly two boy children

Answer 1

1) Let the Probability of randomly meeting a four child family with exactly one child: P(A)

Let the Probability of randomly meeting a four child family with exactly 2 boy children : P(B)

Since the question is about how do we get to the Probability of meeting A or B

We can write:

P(A ∪ B) = P(A) + P(B) - P(A * B)

2) Knowing the subspace. We subtract to not count twice the Probability of A , and B.

If the events are mutually exclusives, i.e. there are no common elements so so we can write that

P(A ∪ B)= P(A) +P(B)