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

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answer is A.

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Detailed Solution

Let n(P)=Number of teachers in Physics.n(M)=Number of teachers in Mathsn(P∪M)=n(P)+n(M)-n(P)-n(P∩M)20=n(P)+12-4⇒n(P)=12.

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