Question

If A and B are finite sets such that n(B) = 10 and A ⊂ B, then find n(A∪B).

Answer 1

Answer: 12

Step-by-step explanation: Using the formula n(A∪B)=n(A)+n(B)−n(A∩B)  then, n(A∩B)=n(A)+n(B)−n(A∪B)

=20+28−36=48−36=12

Answer 2

This problem can be solved by Venn diagram.

Since $A\subset B$, set A belongs to set B.

Thus, $n(A\cup B)=n(B)=10$.