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 teachers teach Physics?

Answer 1

Let A = set of teachers who teach Mathematics

B = set of teachers who teach Physics

∴ n(A ∪ B) = 20, n(A) = 12, n(A ∩ B) = 4

Since n(A ∪ B) = n(A) + n(B) – n(A ∩ B),

20 = 12 + n(B) – 4

∴ n(B) = 12

∴ Number of teachers who teach physics = 12