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An engine moves at the speed of 48 kmph without any coaches attached

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Concentration: Strategy, General Management
GMAT 1: 460 Q35 V20
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An engine moves at the speed of 48 kmph without any coaches attached [#permalink]

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14 Oct 2011, 06:53
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35% (medium)

Question Stats:

70% (01:21) correct 30% (01:42) wrong based on 106 sessions

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An engine moves at the speed of 48 kmph without any coaches attached to it.Speed of the train reduces at the rate that varies directly as the square root of the number of coaches attached.When 4 coaches are attached speed decreases to 36 kmph.What will be the speed of train when 36 coaches are attached.

A ) 24
B ) 36
C ) 12
D ) 0
E ) 18
[Reveal] Spoiler: OA
Manager
Joined: 20 Aug 2011
Posts: 139
Re: An engine moves at the speed of 48 kmph without any coaches attached [#permalink]

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14 Oct 2011, 07:41
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No. of coaches =4
sqr root=2
speed decreases by 12
12=k*2
k=6

No. of coaches=36
swr root=6
decrease=6*6=36
New speed=48-36=12

C
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Joined: 10 Sep 2011
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Concentration: Finance, Strategy
GMAT Date: 12-27-2011
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Re: An engine moves at the speed of 48 kmph without any coaches attached [#permalink]

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14 Oct 2011, 14:40

Explanation:

Here we have to figure out the constant when multiplied with 48 and 1/\sqrt{no. of coach} yields the resultant speed. Lets call the constant C.

Speed reduced from 48 to 36 with inclusion of 4 coached.

48 x 1/\sqrt{4} x C = 36
Solving for C we get C = 3/2.

Now using or equation for final speed : 48 x C x 1/\sqrt{no. of coach}
= 48 x (3/2) x 1/\sqrt{36}
=(48 x 3)/(2 x 6)
=12
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Re: An engine moves at the speed of 48 kmph without any coaches attached [#permalink]

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16 Jan 2017, 00:58
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Re: An engine moves at the speed of 48 kmph without any coaches attached   [#permalink] 16 Jan 2017, 00:58
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