JAMB - Mathematics (2019 - No. 5)
In a class of 50 students, 40 students offered Physics and 30 offered Biology. How many offered both Physics and Biology?
42
20
70
54
Giải thích
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