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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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blowice27
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The XYZ river flows at 12 km/hr. A boy who can row at 2518 m/s [#permalink] New post   04 Oct 2019, 09:52
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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

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Peddi
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Re: The XYZ river flows at 12 km/hr. A boy who can row at 2518 m/s [#permalink] New post   04 Oct 2019, 10:13
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] New post   05 Apr 2020, 08:56
Quote:
.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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I'm not following this part can you please rewrite this out??? TY
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Edwinnguyen
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Re: The XYZ river flows at 12 km/hr. A boy who can row at 2518 m/s [#permalink] New post   05 Apr 2020, 09:44
Width of the river is the ideal route to row but river flows -> it will make the route becomes hypotenuse of perpendicular triangle

Hope it helps

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Re: The XYZ river flows at 12 km/hr. A boy who can row at 2518 m/s [#permalink] New post   05 Apr 2020, 09:48
TY Could you please rewrite the last part of equation so I can see how you solved it?im missing with the A^2+B^2=c^2 solution

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Re: The XYZ river flows at 12 km/hr. A boy who can row at 2518 m/s [#permalink]
05 Apr 2020, 09:48
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