2014 CSAT, all questions
UPSC Prelims 2014 · CSAT
Question 20: Basic Numeracy
A gardener increased the area of his rectangular garden by increasing its length by 40% and decreasing its width by 20%. The area of the new garden
ahas increased by 20%.
bhas increased by 12%.
chas increased by 8%.
dis exactly the same as the old area.
AnswerUPSC’s answer is (b).
Let the old length be L and the old width W, so the old area is LW. The new length is 1.4L and the new width is 0.8W, so the new area is 1.4 x 0.8 x LW = 1.12 LW, a 12 percent increase. For percentage changes in a product, multiply the factors instead of adding the percentages: +40 and -20 do not give +20.
Why each option is right or wrong
- (a) That adds 40 and subtracts 20; changes in a product multiply instead.
- (b) Right. 1.4 x 0.8 = 1.12, a 12 percent increase.
- (c) 8 percent would need a factor of 1.08, which 1.4 x 0.8 does not give.
- (d) The area changes because 1.4 x 0.8 is not equal to 1.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2014, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.