Divide 7 into 291. If the answer is an integer, 7 is a factor.
Divide it. It isn't.
Divide 7 into 291. If the answer is an integer, it's a factor.
Divide 7 into 291. If the result is an integer, 7 is a factor.
I would divide it. It doesn't come out even. It's not a factor.
Add up the digits of 291. If they total a multiple of 9, 9 is a factor.
There isn't an easy test for 7. You have to divide it. 7 is not a factor of 291.
7 doesn't have an easy test. But when I see that 291 is made up of 280 + 11, I know that 7 is not a factor.
Divide 7 into 291. If it comes out evenly, it's a factor. It doesn't, so it's not.
Divide 291 by 7 and see if you get a whole number or is there a remainder. If it is not a whole number, then it is not a factor. 7 goes into 291 41 times with a remainder of 4, so it is not a factor.
You know that 7 isn't a factor of 291 because the quotient of 291 and 7 isn't a whole number.