2021 CSAT, all questions
UPSC Prelims 2021 · CSAT
Question 78: Basic Numeracy
If the price of an article is decreased by 20% and then the new price is increased by 25%, then what is the net change in the price ?
a0%
b5% increase
c5% decrease
dCannot be determined due to insufficient data
AnswerUPSC’s answer is (a).
Take the original price as 100. A 20% decrease gives 80. A 25% increase on 80 adds 20, giving 100. The price is back at the original, so the net change is 0%. Equivalently, 0.8 × 1.25 = 1. Remember: successive percentage changes multiply, and a fall of 20% is undone by a rise of 25%, because 1 ÷ 0.8 = 1.25.
Why each option is right or wrong
- (a) Right: 0.8 × 1.25 = 1, so the price returns to its original value.
- (b) A 5% increase would need a final price of 105; it is 100.
- (c) A 5% decrease would need a final price of 95; it is 100.
- (d) The percentages are enough; the answer does not depend on the original price.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2021, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.