Your food costs are $2,500. your total food sales are $17,500. what percent of your
food sales do the food costs represent?

$2500 is what % of $17,500
$2500 = n% x  $17,500

Well our problem now is that we can move the decimal back two places on a percent that we do not yet know.
However we can move it back on the number we are multiplying n% by.
Here's why:   Sample:  .67 x 52 = 67 x .52  the answer are the same even though I switched the decimal points.
So
2500 = 175n   ($17500 moved back two places)
You get about 14.28% (rounded to the nearest hundredth of a percent)
Alternative method:
 = .1428 (number goes on for 6 digits and then repeats)  .1428 = 14.28%