2020 CSAT, all questions
UPSC Prelims 2020 · CSAT
Question 47: Basic Numeracy
A shop owner offers the following discount options on an article to a customer :
- 1.Successive discounts of 10% and 20%, and then pay a service tax of 10%
- 2.Successive discounts of 20% and 10%, and then pay a service tax of 10%
- 3.Pay a service tax of 10% first, then successive discounts of 20% and 10%
Which one of the following is correct?
a1 only is the best option for the customer.
b2 only is the best option for the customer.
c3 only is the best option for the customer.
dAll the options are equally good for the customer.
AnswerUPSC’s answer is (d).
Treat the marked price as P. Each option multiplies P by the same three factors: 0.9, 0.8 and 1.1 in option 1, 0.8, 0.9 and 1.1 in option 2, and 1.1, 0.8 and 0.9 in option 3. Multiplication does not depend on order, so every option gives P × 0.792. The final price is identical, so the options are equally good.
Why each option is right or wrong
- (a) Option 1 ends at 0.792P, the same as the others.
- (b) Option 2 ends at 0.792P too.
- (c) Option 3 also ends at 0.792P: the tax is a multiplier, and order does not matter.
- (d) Right: all three give 0.792 times the marked price.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2020, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.