In a survey of 50 newspaper readers, 40 read Champion and 30 read Guardian, how many read both papers?

A.
10 
B.
5 
C.
15 
D.
20
Correct Answer: Option D
Explanation
Let C n G = X
n C only = 40 – x
n G only = 30 – x
40 – X + 30 – X = 50
70 – X = 50X = 70 – 50X = 20