UPSC Prelims 2013 · CSAT
Question 64: Basic Numeracy
In a garrison, there was food for 1000 soldiers for one month. After 10 days, 1000 more soldiers joined the garrison. How long would the soldiers be able to carry on with the remaining food ?
AnswerUPSC’s answer is (d).
Food for 1000 soldiers for a month of 30 days is 30,000 soldier-days. After 10 days, 10,000 soldier-days have been eaten and 20,000 remain. With 2000 soldiers now sharing it, the food lasts 20,000 / 2000 = 10 days. The answer counts the remaining food from the day the extra soldiers arrive, not from the start.
Why each option is right or wrong
- (a) Wrong. 25 days for 2000 soldiers would need 50,000 soldier-days.
- (b) Wrong. 20 days would need 40,000 soldier-days.
- (c) Wrong. 15 days would need 30,000 soldier-days, more than remain.
- (d) Right. 20,000 / 2000 = 10 days.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2013, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.