2019 CSAT, all questions
UPSC Prelims 2019 · CSAT
Question 40: Basic Numeracy
The average marks of 100 students are given to be 40. It was found later that marks of one student were 53 which were misread as 83. The corrected mean marks are
a39
b39·7
c40
d40·3
AnswerUPSC’s answer is (b).
The original total is 100 × 40 = 4000. One mark was read as 83 instead of 53, so the total was 30 too high. Corrected total = 4000 - 30 = 3970, and the corrected mean = 3970 / 100 = 39.7. Always correct the total first, then divide again by the number of students.
Why each option is right or wrong
- (a) Wrong: 39 would need a total of 3900.
- (b) Right: 3970 / 100 = 39.7.
- (c) Wrong: 40 ignores the correction.
- (d) Wrong: 40.3 adds the error instead of subtracting it.
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.