Question

In a school, there are 20 teachers who teach
mathematics or physics, Of these, 12
teach
mathematics and 4 teach both physics
and
mathematics How many teach physics?
.​

Answer 1

Step by step :

Number of teachers who teach math or physics =n(M∪P)=20

Number of teachers who teach math = n(M)=12

Number of teachers who teach math and physics =n(M∩P)=4

Find : Number of teachers who teach physics =n(P)=?

Solution :

n(M∪P)=n(m)+n(P)−n(M∩P)

20=12+n(P)−4

20−12+4=n(P)

n(P)=12

hence 12 teacher teach the physics