UPSC Prelims 2013 · CSAT
Question 60: Basic Numeracy
In a rare coin collection, there is one gold coin for every three non-gold coins. 10 more gold coins are added to the collection and the ratio of gold coins to non-gold coins would be 1 : 2. Based on the information, the total number of coins in the collection now becomes
AnswerUPSC’s answer is (a).
Gold to non-gold is 1 : 3, so write gold = k and non-gold = 3k. Adding 10 gold coins gives (k + 10) : 3k = 1 : 2, so 2k + 20 = 3k and k = 20. Now there are 30 gold and 60 non-gold coins, a total of 90. Note that the non-gold coins stay at 60 because only gold coins were added.
Why each option is right or wrong
- (a) Right. 30 gold + 60 non-gold = 90.
- (b) Wrong. A total of 80 gives k = 17.5, not a whole number.
- (c) Wrong. A total of 60 gives k = 12.5, not a whole number.
- (d) Wrong. A total of 50 gives 20 gold : 30 non-gold, which is 2 : 3.
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.