Question

What digits must be added or substracted from $21435$ to make it divisible by $15$?

• A. $0$
• B. $5$
• C. $7$
• D. None of the above.

Answer 1

The correct option is A $0$

For a number to be divisible by $15$, it must be divisible by $3$ as well as $5$.

For a number to be divisible by $3$, sum of its digits must be divisible by $3$.

Also, if the number has $0$ or $5$ at it's unit place then the number is divisible by $5$.

Clearly, the given number $21435$ is divisible by $15$ because sum of it's digit is $15$ which is amultiple of $3$ and there is $5$ at unit place which make it divisible by $5$ as well.

Hence, we can add or substract $0$ or a multiple of 15 in the number to make it divisible by 15.