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Option 2 : 8
Given:
Number of teachers who teach mathematics or physics = n (M ∪ P) = 20
Number of teachers who teach mathematics = n (M) = 12
Number of teachers who teach both mathematics and physics = n (M ∩ P) = 4
Concept:
n (M ∪ P) = n (M) + n (P) - n (M ∩ P)
Calculation:
We need to find the number of teachers who teach physics i.e., n (P)
⇒ n (M ∪ P) = n (M) + n (P) - n (M ∩ P)
⇒ 20 = 12 + n (P) - 4
⇒ n (P) = 12
Number of teachers who teaches only physics = 12 - 4 = 8
Hence, the number of teachers who teach physics is 8.
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