If $A, B$ and $C$ are any three sets, then $A - (B \cap C)$ is equal to

State whether each of the following statement is true or false. Justify you answer.

$\{a, e, i, o, u\}$ and $\{a, b, c, d\}$ are disjoint sets.

If $X$ and $Y$ are two sets such that $X$ has $40$ elements, $X \cup Y$ has $60$ elements and $X$ $\cap\, Y$ has $10$ elements, how many elements does $Y$ have?

Let $A =\{1,2,3,4,5,6,7\}$ and $B =\{3,6,7,9\}$. Then the number of elements in the set $\{ C \subseteq A : C \cap B \neq \phi\}$ is

Let $A=\{a, b\}, B=\{a, b, c\} .$ Is $A \subset B \,?$ What is $A \cup B \,?$

If ${N_a} = \{ an:n \in N\} ,$ then ${N_3} \cap {N_4} = $