If A and B are two sets such that n
Question:

If $A$ and $B$ are two sets such that $n(A)=115, n(B)=326, n(A-B)=47$, then write $n(A \cup B)$.

Solution:

$n(A)=115, n(B)=326$ and $n(A-B)=47$

Now,

$n(A)-n(A \cap B)=n(A-B)$

$\Rightarrow 115-n(A \cap B)=47$

$\Rightarrow n(A \cap B)=68$

Thus, we get:

$n(A \cup B)=n(A)+n(B)-n(A \cap B)$

$=115+326-68$

$=373$