If n(A) denotes the number of elements in the set A and if n(A)=4, n(B)=5 and n(A B)=3, then n[(A B) (B A)] is equal to

JEE Main Mathematics question

If denotes the number of elements in the set and if , and , then is equal to

Answer: (B)

, so its size is .

Question ID VK-003117