MathDB

At summer camp, there are

20

campers in each of the swimming class, the archery class, and the rock climbing class. Each camper is in at least one of these classes. If

4

campers are in all three classes, and

24

campers are in exactly one of the classes, how many campers are in exactly two classes?

\text{(A) }12\qquad\text{(B) }13\qquad\text{(C) }14\qquad\text{(D) }15\qquad\text{(E) }16

9