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

If $A$ and $B$ are two sets such that $n(A)=70, n(B)=60, n(A \cup B)=110$, then $n(A \cap B)$ is equal to

(a) 240

(b) 50

(c) 40

(d) 20

Solution:

(d) 20

We have:

$n(\mathrm{~A} \cap \mathrm{B})=n(\mathrm{~A})+n(\mathrm{~B})-n(\mathrm{~A} \cup \mathrm{B})$

$=70+60-110$

$=20$