You would multiply the sales regular price by the percent and then subtract your answer from the regular sale price. For example, if something cost $499 and the sales price was 15% off, you would multiply 499 by 0.15 and then you would get 74.85. You would then subtract the 74.89 from the original price which was $499 and you would get $424.11 which would be your new price with the discount.