UPSC Prelims 2021 · CSAT
Question 58: Basic Numeracy
In an objective type test of 90 questions, 5 marks are allotted for every correct answer and 2 marks are deducted for every wrong answer. After attempting all the 90 questions, a student got a total of 387 marks. What is the number of incorrect responses ?
AnswerUPSC’s answer is (a).
Let w be the wrong answers; the rest, 90 − w, are correct. Marks = 5(90 − w) − 2w = 450 − 7w = 387, so 7w = 63 and w = 9. Check: 81 correct give 405 and 9 wrong take away 18, leaving 387. Remember: when all questions are attempted, one unknown is enough; start from the full-marks total, and each wrong answer costs 5 + 2 = 7 marks against it.
Why each option is right or wrong
- (a) Right: full marks 450 less 387 is 63, and each wrong answer costs 7, so 9.
- (b) 13 wrong would lose 91, leaving 359.
- (c) 27 wrong would lose 189, leaving 261.
- (d) 43 wrong would lose 301, leaving 149.
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.