UPSC Prelims 2019 · CSAT
Question 16: Basic Numeracy
When a runner was crossing the 12 km mark, she was informed that she had completed only 80% of the race. How many kilometres was the runner supposed to run in this event ?
AnswerUPSC’s answer is (b).
The 12 km already run is 80% of the race, so the full distance is 12 / 0.8 = 15 km. Check: 80% of 15 is 12, and the remaining 3 km is the other 20%. When a part and its percentage are known, divide the part by the percentage as a decimal to get the whole, rather than adding 80% to 12.
How you could have got this
No shortcut here: in a “how many” question, ruling out options doesn’t help. Every statement has to be judged.
Which options go is worked out from UPSC’s key and the options, not by a model.
Why each option is right or wrong
- (a) Wrong: 14 km would make 12 km about 86% of the race.
- (b) Right: 12 is 80% of 15.
- (c) Wrong: 16 km would make 12 km only 75%.
- (d) Wrong: 16.5 km would make 12 km about 73%.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2019, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.