The original price of the shorts was $22.50. I used the calculator and started multiplying numbers by .80 (80%) until I multiplied 22.50 x .80 and it equaled 18. Basically you have to divide the percentage that the problem gives you, in this case 20, by 100 (20/100 = .20). Then find how much it lacks to have 100 (in this case it is 80), when you divide that by 100, you are left with .80. You then start to multiply that by numbers until you get your answer. I'm sure that there is a much simpler way to answer this math problem but this is the only way I can think right now of solving it. I hope this helps you!!