In a class of 40 students, 32 offer mathematics, 24 offer physics and 4 offer neither mathematics nor physics. How many offer both mathematics and physics?
A.
4
B.
8
C.
16
D.
20
Correct answer is D
40 = 32 - x + x + 24 + 4
40 = 60 - x
x = 60 - 40
x = 20