Question

In a survey of 100 women,
34 use shampoo A
42 use shampoo B
31 use shampoo C
9 use shampoo A&B
10 use shampoo A&C
6 use shampoo B&C
2 use all three

How many use shampoo A & C, but not B?

Answer 1

10 use A&C (may or may not use B)
2 use all three (A, B & C)
So how many use A & C but not B?