In the following probability distribution (in table form), the discrete random variable X represents the number of activities the mother of a 6th-8th grade student is involved in.

x P(X = x)

0 0.10

1 0.137

2 0.27

3 0.302

4 0.191

a) Find the probability that a randomly selected mother is involved in at least two activities.

b) Find the probability that a randomly selected mother is involved in exactly three activities, given that she is involved in at least two activities.