First slide

Operations on Sets

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

Easy

A

12
B

8
C

16
D

None of these

Solution

Let $n (P) =$ Number of teachers in Physics.
$n (M) =$ Number of teachers in Maths
$n (P \cup M) = n (P) + n (M) - n (P) - n (P \cap M)$
$20 = n (P) + 12 - 4 \Rightarrow n (P) = 12 .$

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