Percent of a Number

A percent is just multiplication in disguise. 15% of 200 means 0.15 times 200, which is 30. The word "of" almost always means multiply. So slide the decimal two places left, then multiply.

The fast way is to build from chunks. To find 10%, move the decimal one place left: 10% of 350 is 35. Need 5%? Halve that, so 17.5. Need 15%? Add them: 52.5. Servers learn this on day one. Stack 10% and 1% pieces and you can run tips, taxes, and discounts in your head.