My mother bought a dress for Xiao Hong. Now it's 20% off in the mall. It's 15 yuan cheaper than the original price. How much is the present price of this dress?

My mother bought a dress for Xiao Hong. Now it's 20% off in the mall. It's 15 yuan cheaper than the original price. How much is the present price of this dress?

Assume that the original value payable is X
According to the theme
0.8x = X-15 (or 0.2x = 15)
The solution is x = 75