In a class of 50 students, 40 students offered Physics and 30 offered Biology. How many offered both Physics and Biology?

A. 42
B. 20
C. 70
D. 54

Correct Answer: Option B

B. 20

Explanation

n(Total) = 50

n(Physics) = 40

n(Biology) = 30

Let n(Physics and Biology) = x

n(Physics only) = 40 -x

n(Biology only) = 30 – x

40 – x + 30 – x + x = 50

70 – x = 50

x = 20