Coz it's values aren't changing both ways. it's just a change in the order of multiplication.
12 * (1/100) * 50 = 50 * (1/100) * 12
Was looking for this. I don't remember when I learned percentages were just multiply and move the decimal twice, but it has never left my brain and it has been immensely helpful for quick maths.
How do other people do it if they don’t “multiply and move decimal points around”