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

Given :


20 teachers teach physics or math.


4 teachers teach physics and math.


12 teach maths


Let us denote teachers who teach physics as n(P) and for Maths n(M).


Now ,


20 teachers teach physics or math = n(P M) = 20


4 teachers teach physics and math = n (P M) = 4


12 teach maths = n(M) =12


We know,


n (P M) = n(M) + n(P) – n (P M)


Substituting the values we get


20 = 12+n(P)–4


20 = 8+ n(P)


n(P) =12


There are 12 physics teachers.


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