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A retailer charges 18% GST on the full marked price of ₹5000 instead of on the price after the promised 10% discount. By how much is the customer overcharged?

Class 8Comparing QuantitiesComparing Quantities
  • A₹500
  • B₹810
  • C₹90
  • D₹900

Step-by-Step Solution

Correct route: SP = and GST = 18% of 4500 = 810. Wrong route: GST = 18% of 5000 = 900. Overcharge = 900 − 810 = 90. Trap: ₹500 is the discount, ₹810 the correct tax and ₹900 the wrong tax — the question asks for the DIFFERENCE. Tax always goes on the discounted price.
Answer: C) ₹90

Key idea: Discount

A discount is a reduction off the **marked price** (MP), not the cost price. The selling price (SP) is what the customer actually pays.

**SP = MP − Discount**
**Discount % = (Discount / MP) × 100**

Example: shirt MP ₹800, discount 25%. Discount amount = 25% of 800 = 200. SP = 800 − 200 = 600.

Note: discount % is calculated on MP. Profit/loss % (Class 7) is on CP. Don't mix them up.

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