UPSC Prelims 2015 · CSAT
Question 79: Basic Numeracy
In a box of marbles, there are three less white marbles than the red ones and five more white marbles than the green ones. If there are a total of 10 white marbles, how many marbles are there in the box ?
AnswerUPSC’s answer is (b).
White marbles are 10. Whites are three fewer than reds, so reds are 10 + 3 = 13. Whites are five more than greens, so greens are 10 − 5 = 5. Total marbles = 10 + 13 + 5 = 28. Take care with direction: when one colour is fewer than another, the other colour is the larger count.
How you could have got this
No shortcut here: in a “how many” question, ruling out options doesn’t help. Every statement has to be judged.
Which options go is worked out from UPSC’s key and the options, not by a model.
Why each option is right or wrong
- (a) Wrong: 26 is less than 10 + 13 + 5.
- (b) Right: 10 + 13 + 5 = 28.
- (c) Wrong: 32 is more than 10 + 13 + 5.
- (d) Wrong: 36 is more than 10 + 13 + 5.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2015, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.