Question

Question 7
Explain why $3\times 5\times 7+7$ is a composite number.

Answer 1

We have,
$a=3\times 5\times 7+7=7(3\times 5+1)=7\times 16$
Since, a has more than two factors (as 1, 7, 16 and a are factors).
So, it is a composite number.

Note: Prime numbers has only two factos 1 and number itself.