UPSC Prelims 2022 · CSAT
Question 69: Basic Numeracy
There are two containers X and Y. X contains 100 ml of milk and Y contains 100 ml of water. 20 ml of milk from X is transferred to Y. After mixing well, 20 ml of the mixture in Y is transferred back to X. If m denotes the proportion of milk in X and n denotes the proportion of water in Y, then which one of the following is correct?
AnswerUPSC’s answer is (a).
After the first move, X has 80 ml milk and Y holds 120 ml, one-sixth of it milk. The 20 ml returned to X carries 10/3 ml milk and 50/3 ml water. X now has 80 + 10/3 = 250/3 ml milk in 100 ml, so m = 5/6. Y holds 100 ml, of which 100 − 50/3 = 250/3 ml is water, so n = 5/6. Hence m = n.
Why each option is right or wrong
- (a) Correct: both proportions equal 5/6.
- (b) Wrong: m is not larger; both are 5/6.
- (c) Wrong: m is not smaller; both are 5/6.
- (d) Wrong: the data given is enough.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2022, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.