Question

If $A=\{x:xϵW,3\le x<6\},B=\{3,5,7\}$ and $C=\{2,4\}$;

find :$n(A-B)$.

Answer 1

Given : $A=\{x:xϵW,3\le x<6\},B=\{3,5,7\}$ and $C=\{2,4\}$

$\Rightarrow A=\{3,4,5\}$
Now, $A-B$ means removing the elements of $B$ which are in $A$

$\therefore A-B=\left\{4\right\}$ as $3,5$ are common elements of $A$ and $B$.

Hence, $n(A-B)=1$.