UPSC Prelims 2016 · CSAT
Question 51: Basic Numeracy
The sum of the ages of 5 members comprising a family, 3 years ago was 80 years. The average age of the family today is the same as it was 3 years ago, because of an addition of a baby during the intervening period. How old is the baby ?
AnswerUPSC’s answer is (b).
Three years ago the 5 members summed to 80, so the average was 16. Today those 5 are each 3 years older: 80 + 15 = 95. The average is still 16 with 6 members, so the total is 96. Baby = 96 - 95 = 1 year. Remember: the old members add 3 years each, and the newcomer's age makes up the balance.
Why each option is right or wrong
- (a) Six months would make the total 95.5, not 96.
- (b) Right: 96 - 95 = 1 year.
- (c) 2 years would make the total 97.
- (d) 2 years 6 months would make the total 97.5.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2016, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.