Quantitative Aptitude – TSD – Swati can row a boat on still water at a

XAT 2021 Exam Paper – Quantitative Aptitude – TSD – Swati can row a boat on still water at a

Q. Swati can row a boat on still water at a speed of 5 km/hr. However, on a given river, it takes her 1 hour more to row the boat 12 km upstream than downstream. One day, Swati rows the boat on this river from X to Y, which is N km upstream from X. Then she rows back to X immediately. If she takes at least 2 hours to complete this round trip, what is the minimum possible value of N?

1. 2
2. 2.1
3. 4.8
4. 3.6
5. 3

Answer: 4.8

Solutions:
let the speed of stream = x
From the question,
12/(5-x)-12/(5+x)=1
on solving ,(5+x-5+x)/(25-x^2 )=1/12
x^2+24x-25=0
(x+24)(x-1)= 0
Or x = -24 or 1
As x can not be negative so x =1
As per question ,
N/(5+x)+N/(5-x)≥2
N/6+N/4≥2
5N/12≥2
N≥24/5=4.8
Thus minimum value of N = 4.8

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