Probability of independent events

Probability that student A can solve the problem=1/3 Probability that student B can solve the problem=1/5 Probability that only one of them can solve the problem=? How would you solve this problem? I thought since they are independent events, p(AUB)= p(A)+P(B)-p(A and B)= 1/3+1/5-1/3.1/5= 7/15 but i...