A 10 percent discount and a 10 percent fee can be calculated in either order but they don’t cancel out.

Example, 90% of (110% of 10) = 110% of (90% of 10). But neither of those is evaluates to 10. It evaluates to 9.9.

For any percentage X, and and base value C,(100 - X)% x ((100 + X)% x C) = (100 + X)% x ((100 - X)% x C) = (100 - (X^2/100))% x C