P(B) = 1/3

P(A|B) = 1/5

(Question) calculate the probability that only one event occurs.

i have already calculated that the P(A&B) = P(B) x P(A|B) = 1/15

P(A'&B') = 0.2 from the following

P(AorB) = (P(A) + P(B) - (PA&B)

so

1 - P(AorB) = P(A'&B')

i thought the answer to the question would be (P(A') x P(B)) + (P(A) x P(B')) but that doesnt work.

Note: the answer is suppose to be 11/15

I would really appreciate any help on this.