Find the overall percent change compared to the original amount: A shirt originally costing $20 is marked with a 15% discount.

$17

Step-by-step explanation:

15% is the same as 0.15. When you get a 15% reduction, it's the same as multiplying the original number by 0.85 (85%, the leftover from a 15% reduction). This means you simply do 20*0.85 to get the answer.