Step-by-step explanation:
step 1. the sale is 20% off; that means times 0.8.
step 2. the additional coupon is 10% off of the sale price; that means times 0.9.
step 3. so the final price is (0.8)(0.9) times the retail price
step 4. (0.8)(0.9) = 0.72 or a 28% discount and not 30%.
