Question

If n(A-B)=18,n(AuB)=70 and n(AnB)=25 then find n(B)

Answer 1

n(A-B) denotes elements which are in A but not in B

n(Au B) denotes elements in A and B

n(AnB) denotes elements that are common in A and B

Now I will add one more set

n(B-A) which denotes elements in B but not in A

So, n(AuB) = n(A-B) + n( B-A) +n(AnB)

70 = 18 +n(B-A) + 25

70 = 43 + n(B-A)

n(B-A) = 70-43

n(B-A) = 27

So, n(B) = n( B-A) + n( AnB)

= 27+25

= 52