Question

20 teachers of a school either teach mathematics or physics. 12 of them teach mathematics while 4 teach both the subjects. Then the number of teachers teaching physics only is.

• A. 12
• B. 8
• C. 16
• D. None of these

Answer 1

Answer: (A)

12

Answer 2

Let $n ( P )$= Number of teachers in Physics.

$n ( M )$= Number of teachers in Maths

$n ( P \cup M ) = n ( P ) + n ( M ) - n ( P \cap M )$

$20 = n ( P ) + 12 - 4$ ⇒ $n ( P ) = 12$.