Speed Distance : GMAT Problem Solving (PS)
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# Speed Distance

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Manager
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14 Oct 2011, 06:53
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Difficulty:

35% (medium)

Question Stats:

72% (02:14) correct 28% (02:08) wrong based on 43 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
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14 Oct 2011, 07:41
1.
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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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
Re: Speed Distance   [#permalink] 14 Oct 2011, 14:40
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