Question

There are 260 persons with skin disorders. If 150 had been exposed to the chemical A, 74 to the chemical B, and 36 to both chemicals A and B, find the number of persons exposed to Chemical B but not Chemical A.

Answer 1

Let A = set of persons exposed to chemical A

B = set of persons exposed to chemical B

X = set of all persons

∴ n(X) = 260, n(A) = 150, n(B) = 74, n(A ∩ B) = 36

No. of persons exposed to chemical B but not to chemical A
= n(A' ∩ B)
= n(B) - n(A ∩ B)
= 74 – 36
= 38