Question

Check whether the number $12345321$ is divisible by $3$. Is it divisible by $9$?

Answer 1

If the sum of the digits of a number are divisible by $3$, then the number itself is also divisible by $3$.

The sum of the digits $=1+2+3+4+5+3+2+1=21$

Since, $21$ is divisible by $3$, so the number is also divisible by $3$.

Similarly, if the sum of the digits of a number are divisible by $9$, then the number itself is also divisible by $9$.

The sum of the digits $=1+2+3+4+5+3+2+1=21$

Since, $21$ is not divisible by $9$, so the number is also not divisible by $9$.

Hence, the given number is divisible by $3$ but not by $9$.