UPSC Prelims 2015 · CSAT
Question 15: Basic Numeracy
In a test, a candidate attempted only 8 questions and secured 50% marks in each of the questions. If he obtained a total of 40% in the test and all questions in the test carried equal marks, how many questions were there in the test ?
AnswerUPSC’s answer is (b).
Attempting 8 questions at 50% each earns the equivalent of 4 full questions. Let each question carry m marks and the test have N questions. Marks obtained = 4m, which is 40% of the total Nm. So 4m = 0.4 × Nm, giving N = 4 ÷ 0.4 = 10 questions.
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: 4 out of 8 would be 50%, not 40%.
- (b) Right: 4 ÷ 10 = 40%.
- (c) Wrong: 4 out of 15 is about 26.7%.
- (d) Wrong: 4 out of 16 is 25%.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2015, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.