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UPSC CSE CSAT 2020 · Question 47 · Arithmetic: percentage, ratio, averages, time & work

A shop owner offers the following discount options on an article to a customer:

CSAT 2020 · Q47

Arithmetic: percentage, ratio, averages, time & work Easy

A shop owner offers the following discount options on an article to a customer:

  1. 1.Successive discounts of 10% and 20%, and then pay a service tax of 10%
  2. 2.Successive discounts of 20% and 10%, and then pay a service tax of 10%
  3. 3.Pay a service tax of 10% first, then successive discounts of 20% and 10%

Which one of the following is correct?

Answer & explanation

Answer: (d) All the options are equally good for the customer.

Each option multiplies the price by the same three factors — 0·9, 0·8 and 1·1 — only in a different order. Multiplication does not depend on order, so the customer pays the same in every case.

  1. Take the price as ₹ 100.
  2. Option 1: 100 × 0·9 × 0·8 × 1·1 = ₹ 79·2.
  3. Option 2: 100 × 0·8 × 0·9 × 1·1 = ₹ 79·2.
  4. Option 3: 100 × 1·1 × 0·8 × 0·9 = ₹ 79·2.
  5. All three cost the same, so all options are equally good.

Remember · Successive percentage changes are multiplying factors; their order never changes the final result.

Question and answer: UPSC's official GS Paper II (2020, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·

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