Answer:
The answer to your question is 25%
Step-by-step explanation:
Data
Original price = $120
Price after discount = $90
Discount = ?
Process
1.- Consider that the original price is the 100% and use a rule of three to find the percent of discount
$120 ----------------- 100%
$90 ---------------- x
x = (90 x 100) / 120
x = 9000 / 120
x = 75%
2.- Calculate the percent of discount
$90 represents 75% of the original price, then,
Percent of discount = 100 -75
= 25 %