Answer :
Given: n(A) = 54, n(B) = 39, n(B – A) = 13
Using the hint
n(B) = n(B – A) + n(A ∩ B)
⇒ 39 = 13 + n(A ∩ B)
⇒ n(A ∩ B) = 39 – 13
⇒ n(A ∩ B) = 26
Visualizing the hint given,
We know that n(A ∪ B) = n(A) + n(B) – n(A ∩ B)
⇒ n(A ∪ B) = 54 + 39 – 26
⇒ n(A ∪ B) = 67
Hence n(A ∪ B) = 67
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