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# The XYZ river flows at 12 km/hr. A boy who can row at 2518 m/s

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Manager
Joined: 16 Apr 2019
Posts: 117
Location: India
Concentration: Marketing, Sustainability
GPA: 4
WE: Information Technology (Computer Software)
The XYZ river flows at 12 km/hr. A boy who can row at 2518 m/s  [#permalink]

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04 Oct 2019, 08:52
1
2
00:00

Difficulty:

55% (hard)

Question Stats:

50% (02:07) correct 50% (02:48) wrong based on 14 sessions

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The XYZ river flows at 12 km/hr. A boy who can row at 25/18 m/s in still water had to cross it in the least possible time. The distance covered by the boy is how many times the width of the river XYZ?

A. 2.1
B. 2.3
C. 2.6
D. 2.9
E. 3.0
Manager
Joined: 20 Jul 2019
Posts: 59
Re: The XYZ river flows at 12 km/hr. A boy who can row at 2518 m/s  [#permalink]

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04 Oct 2019, 09:13
blowice27 wrote:
The XYZ river flows at 12 km/hr. A boy who can row at 25/18 m/s in still water had to cross it in the least possible time. The distance covered by the boy is how many times the width of the river XYZ?

A. 2.1
B. 2.3
C. 2.6
D. 2.9
E. 3.0

Speed of the river XYZ = 12 kmph

Speed of the boy = 5 kmph

Let the time taken by the boy to cross the river in still water = T

Width of the river = 5T
The boy takes the least time when he is travelling directly across the river.

But the river current pushes him in a direction perpendicular to the flow,
Distance travelling along the river = 12T

Effective distance travelled by boy = √(12T)2+(5T)2=13T

Distance covered by the boy
width of the river
=
13T
5T
= 2.6

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Re: The XYZ river flows at 12 km/hr. A boy who can row at 2518 m/s   [#permalink] 04 Oct 2019, 09:13
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