Calculating the original number after a percentage increase. 400 100 percent - 20 percent x original price 100 percent minus 20 percent is 80 percent or 08. The problem you are probably struggling with is this.
The problem you are probably struggling with is this.
To find the actual discount multiply the discount rate by the original amount x. Find out number before percentage was added on. Add 100 percent to the sales tax rate. Hint if you start with a value of x subtracting 9 gives you 91 of the original value because 100 9 91.