taking x% is just multiplying by x/100, and multiplication is commutative. x% of y is just y×x×1/100, which is the same as x×y×1/100

you can also ignore the % and divide by 100 at the end. for example, what’s 5% of 5? that might take a minute to work out. what’s 25/100? you instantly know it’s 1/4