If $aN = \{ ax : x \in N \}$,then the set $3N \cap 7N$ is equal to .....$N$.

Let $A = \{1, 2, 3\}$. The total number of distinct relations that can be defined over $A$ is

In a town of $10,000$ families,it was found that $40\%$ of families buy newspaper $A$,$20\%$ buy newspaper $B$,$10\%$ buy newspaper $C$,$5\%$ buy $A$ and $B$,$3\%$ buy $B$ and $C$,and $4\%$ buy $A$ and $C$. If $2\%$ of families buy all three newspapers,then the number of families that buy newspaper $A$ only is:

Which of the following sets is non-empty?

If $A = \{1, 2, 3, 4, ..., 100\}$ and $B = \{51, 52, 53, ..., 180\}$,then the number of elements in $(A \times B) \cap (B \times A)$ is:

If $n(A) = 4$,$n(B) = 3$,and $n(A \times B \times C) = 24$,then $n(C) = $