Question

If n(B) = 17, n(A B) = 30, and n(A �¿ B) = 4, find n(A).

Answer 1

If you mean

n(B) = 17, n(A∪B) = 30, and n(A∩B) = 4

Then since

n(A∪B) = n(A)+n(B)-n(A∩B)

30 = n(A) + 17 - 4
n(A) = 17