Discount questions involve three prices. The cost price (CP) is what the shopkeeper paid. The marked price (MP), also called the list or tag price, is what is printed on the item. The selling price (SP) is what the customer finally pays after the discount.
- Discount = MP − SP, and the discount percentage is on MP.
- Profit = SP − CP, and the profit percentage is on CP.
Almost every mistake in this chapter comes from mixing up those two bases. Hold on to them and the questions become routine.
Worked example 1: SP from MP
A shirt is marked ₹1,200 and sold at a 15% discount. SP = 1,200 × 0.85 = ₹1,020.
Worked example 2: MP from SP
After a 15% discount a pair of shoes costs ₹1,360. MP = 1,360 ÷ 0.85 = ₹1,600. Do not add 15% to the SP: the discount was a percentage of the larger MP.