Easy. Follow these steps:

1. Take the last digit of the number you’re testing and double it.

2. Subtract this number from the rest of the digits in the original number.

-If this new number is either 0 or if it’s a number that’s divisible by 7, then you know that the original number is also divisible by 7.

-If you can’t easily tell yet if the new number is divisible by 7, go back to the first step with this new smaller number and try again.

For example:

Is 345 divisible by 7?

Let’s use the three-step-process to find out.

1. Last digit: 5

double it: 10

2. Subtract 10 from the rest of the digits. 34-10=24

– this is not 0 not a number divisible by 7.

So 345 is not divisible by 7!

Let’s try another one: 175

1. Last digit 5

2. Double it:10

3. 17-10=7— IT’S DIVISIBLE BY 7!

Easy and fun? Try it yourself!