Divisibility Rule for 7
If you divide a number by 7 and you get a whole number as an answer (quotient), then that number is divisible by 7.
Instead of simply dividing your number by 7 to see if you get a whole number, you can use what we call the Divisibility Rule for 7.
The Divisibility Rule for 7 is used to determine if a number is divisible by 7. You can also call it the test of divisibility for 7.
You can determine if a number is divisible by 7 by grouping the numbers in blocks of three from right to left.
Then alternate subtracting and adding the numbers in the blocks. If the result is a multiple of 7, then it is divisible by 7.
Take 2,659,937 as an example: 937 - 659 + 2 = 280. Since 280 is a multiple of 7, you know that 2,659,937 is divisible by 7.
However 3,659,937 is not divisible by 7 because when we calculate 937 - 659 + 3 = 281, we see that the result is 281 which is not a multiple of 7.