If S and T are two sets such that S has 21 elelments, T has 32 elements and S∩T had 11 elements, how many elements does S∪T have?
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Solution
Given : n(S)=21,n(T)=32,n(S∩T)=11
Solve for n(S∪T) n(S∪T)=n(S)+n(T)−n(S∩T) ⇒n(S∪T)=21+32−11 ⇒n(S∪T)=53−11 ⇒n(S∪T)=42
Thus, the set (S∪T) has 42 elements.