Question

What is the rule of divisibility by 7?

Answer 1

Please see below.

Explanation:

Starting from right mark off the digits in groups of threes (just as we do when we put commas in large numbers).

Now add up alternate group of numbers and find the difference between the two. If the difference is divisible by `7`, entire number is divisible by `7`.

For example `123456789113`, these are grouped as `123`, `456`, `789` and `113`

and `123+789=912` and `456+113=569`.

As difference between `912-569=343`

As `343` is divisible by `7`, `123456789113` is divisible by `7`