Question

3. If A, B n(B) = aredisjoint setssuch that n(A) = 4 , n(A cup B)=7 then answer is​

Answer 1

By definition of disjoint set we mean that there won’t be any common elements in both the sets. Therefore A intersection B will be null.

∴  n(A∩B)=0

⇒  n(A∪B)=n(A)+n(B)−n(A∩B)

⇒  n(A∪B)=n(A)+n(B)−0

⇒  n(A∪B)=n(A)+n(B)−0

∴  A∪B=A+B