X and Y are two sets such that n(X) = 15, n(Y) = 12 and n{X ∩ Y} = 7. Find ∩{X ∪ Y}
A
21
B
225
C
15
D
20
Verified Correct Answer: D.
Step-by-Step Mathematical Solution
n(X ∪ Y) = n(X) + n(Y) − n(X ∩ Y)
= 15 + 12 − 7
∴ n(X ∪ Y) = 20
Source: Myschool Past Questions Archive (Record #40616)