Question

If n(a)=3 , n(b)=5 , n(a intersection b)=2 then find n(a?b).

Answer 1

n(a union b) = n(a)+n(b)-n(a intersection b)
so let n(a union b) is x
x=3+5-2
x=8-2
x=6
n(a union b) = 6