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# Source : GMATPrep At a certain instant in time, the number

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VP
Joined: 30 Jun 2008
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Source : GMATPrep At a certain instant in time, the number [#permalink]

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11 Oct 2008, 09:54
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Difficulty:

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Question Stats:

100% (04:23) correct 0% (00:00) wrong based on 6 sessions

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Source : GMATPrep

At a certain instant in time, the number of cars, N , traveling on a portion of a certain highway can be estimated by the formula

N=( 20*L*d)/(600+s^2)

where L is the number of lanes in the same direction, d is the length of the portion of the highway, in feet, and s is the average speed of the cars, in miles per hour. Based on the formula, what is the estimated number of cars traveling on a 21 mile portion of the highway if the highway has 2 lanes in the same direction and the average speed of the cars is 40 miles per hour? (5,280 feet = 1 mile)
(A) 155
(B) 96
(C) 80
(D) 48
(E) 24
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Kudos [?]: 728 [0], given: 1

Manager
Joined: 27 Sep 2008
Posts: 76

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Re: PS: Estimated number of Cars [#permalink]

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11 Oct 2008, 10:48
could you copy & paste the screenshot ?

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Manager
Joined: 10 Aug 2008
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Re: PS: Estimated number of Cars [#permalink]

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11 Oct 2008, 10:58
Not able to solve, can anybdy help me out ?

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VP
Joined: 30 Jun 2008
Posts: 1032

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Re: PS: Estimated number of Cars [#permalink]

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11 Oct 2008, 11:13
I am not sure if I posted the question right. No screen-shot available

I googled to find this http://www.manhattangmat.com/forums/at- ... t4743.html

but not much help there I guess
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"You have to find it. No one else can find it for you." - Bjorn Borg

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SVP
Joined: 29 Aug 2007
Posts: 2471

Kudos [?]: 855 [0], given: 19

Re: PS: Estimated number of Cars [#permalink]

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11 Oct 2008, 17:25
amitdgr wrote:
Source : GMATPrep

At a certain instant in time, the number of cars, N , traveling on a portion of a certain highway can be estimated by the formula

N=( 20*L*d)/(600+s^2)

where L is the number of lanes in the same direction, d is the length of the portion of the highway, in feet, and s is the average speed of the cars, in miles per hour. Based on the formula, what is the estimated number of cars traveling on a 21 mile portion of the highway if the highway has 2 lanes in the same direction and the average speed of the cars is 40 miles per hour? (5,280 feet = 1 mile)
(A) 155
(B) 96
(C) 80
(D) 48
(E) 24

N = (20*L*d)/(600+s^2)
N = (20*2*21x5280)/(600+40^2)
N = (20*2*21x5280)/2200
N = (2*21x48)
N = 96*21

Answer might be B but all answer choices are wrong because N is 96x21. The GmatPrep might have forgotten to include 21 in neumerator and simply put 5280.

I think I saw this question earlier but do not remember whether it was solved.
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Kudos [?]: 855 [0], given: 19

Manager
Joined: 05 Oct 2011
Posts: 169

Kudos [?]: 55 [0], given: 62

Re: Source : GMATPrep At a certain instant in time, the number [#permalink]

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18 Nov 2011, 12:32
First convert the feet to mile. So 1 mile = 5280 feet.
1/2 mile = 2640 feet
So substituting the values in given formula
(10 * 2 * 2640)/(1600 + 600)

= 48

ans: D

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Manager
Joined: 20 Oct 2011
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Kudos [?]: 34 [0], given: 11

Concentration: Sustainability, General Management
GMAT 1: 710 Q49 V38
GPA: 3.98
Re: Source : GMATPrep At a certain instant in time, the number [#permalink]

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18 Nov 2011, 13:58
This is a question from OG12 (#68) and is pretty straightforward. You have not copied it correctly which is why it is stumping everyone.

The correct question states "At a certain instant in time, the number of cars, N,
traveling on a portion of a certain highway can be
estimated by the formula (as given)

where L is the number of lanes in the same direction,
d is the length of the portion of the highway, in feet,
and s is the average speed of the cars, in miles per
hour. Based on the formula, what is the estimated
number of cars traveling on a 1/2-mile portion of the
highway if the highway has 2 lanes in the same
direction and the average speed of the cars is 40
miles per hour? (5,280 feet = 1 mile)"

So the portion is 1/2 mile NOT 20 miles. And thus the correct answer is D, after just plugging in numbers and converting 1/2 mile to feet.

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Manager
Joined: 06 Jun 2013
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Kudos [?]: 17 [0], given: 314

Location: India
Concentration: Finance, Economics
Schools: Tuck
GMAT 1: 640 Q49 V30
GPA: 3.6
WE: Engineering (Computer Software)
Re: Source : GMATPrep At a certain instant in time, the number [#permalink]

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17 Oct 2015, 01:48
this question is wrongly copied. instead of 21 miles, instead of 21 miles, it should be 1/2 miles.

Kudos [?]: 17 [0], given: 314

Re: Source : GMATPrep At a certain instant in time, the number   [#permalink] 17 Oct 2015, 01:48
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# Source : GMATPrep At a certain instant in time, the number

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