Divisible by 7

Subtract twice the unit-digit from the 'rest of the number'.

If the result is divisible by 7, the number is divisible by 7.

Example: .Is divisible ny ?

We have: .

. . Since is divisible by , then is divisible by

The procedure can be repeated for larger numbers.

Example: .Is divisible by ?

. . We have: .

Is divisible by ?

. . We have: .

Since is divisible by , then is divisible by