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
Verified Correct Answer: B.
Step-by-Step Mathematical Solution
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
Source: Myschool Past Questions Archive (Record #54947)