Question

If $aN=\{ax:xϵN\}$, then the set $3N\cap 7N$ is

• A. $21N$
• B. $10N$
• C. $4N$
• D. None of these

Answer 1

The correct option is A $21N$

We are to describe the set $3N$ intersection $7N.$

We know that the $L.C.M$. of $3$ and $7$ is $21$.

So, we have $3N\cap 7N$

={$3x:x\in N$}$\cap${$7x:x\in N$}

={$21x:x\in N$}

=$21N$

Thus, the answer is $21N$