UPSC Prelims 2013 · CSAT
Question 31: Basic Numeracy
There are some balls of red, green and yellow colour lying on a table. There are as many red balls as there are yellow balls. There are twice as many yellow balls as there are green ones. The number of red balls
AnswerUPSC’s answer is (b).
Let the number of green balls be g. Yellow balls are twice the green ones, so yellow = 2g. Red balls equal yellow balls, so red = 2g. Red is therefore double the green. It is not the sum of yellow and green (3g) nor yellow minus green (g). The actual counts are unknown, but the relation between red and green is fixed, so it can be stated.
Why each option is right or wrong
- (a) Wrong. Yellow plus green is 3g, while red is 2g.
- (b) Right. Red = yellow = 2g, double the green balls.
- (c) Wrong. Yellow minus green is g, not 2g.
- (d) Wrong. The relation of red to green is fixed even though the numbers are not.
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.