2020 CSAT, all questions
UPSC Prelims 2020 · CSAT
Question 74: Basic Numeracy
A man takes half time in rowing a certain distance downstream than upstream. What is the ratio of the speed in still water to the speed of current?
a1 : 2
b2 : 1
c1 : 3
d3 : 1
AnswerUPSC’s answer is (d).
Let the speed in still water be x and the speed of the current y. Downstream speed is x + y and upstream speed is x - y. For the same distance, half the time downstream means double the speed: x + y = 2(x - y). So x = 3y, giving x : y = 3 : 1.
Why each option is right or wrong
- (a) 1:2 would make the current faster than the boat, so it could not row upstream.
- (b) 2:1 gives speeds 3 and 1, a ratio of 3, not 2.
- (c) 1:3 also has the current faster than the boat.
- (d) Right: speeds 4 and 2 are in the ratio 2:1.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2020, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.