Discounts

A jacket costs 90 dollars and the shop takes 20% off. The discount is 20% of the price, 20% × 90, which is 18 dollars. You pay the price minus the discount, so the sale price is 90 - 18, which is 72 dollars.

On the board, write both steps in one line with a letter for the sale price: s = 90 - 20% × 90. Multiplication goes before subtraction, so the discount is worked out first, and the next line is s = 72.

There is a second route worth knowing. 20% off means you still pay 80% of the price, and 80% of 90 is 72 too. Both routes give the same answer; the first one shows the discount on its own, which is what a receipt prints.