1. 

Remove the last digit, multiply it by 2, and subtract that from the revised number:

2. 

Repeat until you're left with a number that is either a multiple of 7 or not a multiple of 7:

Forty-nine is a multiple of 7. Therefore, the number 55,762 is divisible by 7. Notice that this test looks at least as long, if not longer, than actually dividing the number by 7. Still, it is interesting to do these tests, because it tells us more about how numbers relate to one another.