Question

If n(a u b) = 18, n(a - b) = 5, n(b - a) = 3, find n(a n b)

Answer 1

n(a u b)=n(a - b)+n(b - a)+n(a n b)
18=5+3+n(a n b)
n(a n b)=18-8
n(a n b)=10