JAMB - Mathematics (2010 - No. 4)
In a survey of 50 newspaper readers, 40 read Champion and 30 read Guardian, how many read both papers?
10
5
15
20
Giải thích
Let C n G = X
n C only = 40 - x
n G only = 30 - x
40 - X + 30 - X + X = 50
70 - X = 50
X = 70 - 50
X = 20