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Speed Distance

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Manager
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Status: Do till 740 :)
Joined: 13 Jun 2011
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Concentration: Strategy, General Management
GMAT 1: 460 Q35 V20
GPA: 3.6
WE: Consulting (Computer Software)
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Speed Distance [#permalink] New post 14 Oct 2011, 06:53
00:00
A
B
C
D
E

Difficulty:

  45% (medium)

Question Stats:

67% (01:52) correct 33% (02:06) wrong based on 9 sessions
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
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Status: Meh, I can't take the GMAT before 2017.
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Re: Speed Distance [#permalink] New post 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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Re: Speed Distance [#permalink] New post 14 Oct 2011, 14:40
Answer: Option C = 12

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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