What must be true for p (a and b) = p(a) x p(b)? a. a and b cannot be independent. b. a and b must be disjoint. c. a and b must be independent. d. a and be cannot be disjoint. e. it is always true.

Choice C) A and B must be independent



In general, 
P(A and B) = P(A)*P(B|A)
and
P(A and B) = P(B)*P(A|B)

The only time P(A) = P(A|B) and P(B) = P(B|A) are true is when A and B are independent. In other words, one event occurring does not alter the probability of the other event.