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# At a certain instant in time, the number of cars, N

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Director
Joined: 09 Mar 2016
Posts: 940
Re: At a certain instant in time, the number of cars, N  [#permalink]

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11 Nov 2017, 09:25
Bunuel wrote:
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

$$N=\frac{20Ld}{600+s^2}$$

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 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)

(A) 155
(B) 96
(C) 80
(D) 48
(E) 2

Given:
L = 2 lanes;
d = 1/2*5,280 feet;
s = 40 miles per hour.

Thus, $$N=\frac{20*2*\frac{1}{2}*5,280}{600+40^2}=48$$.

Bunuel hello, one question; Why did you write so d = 1/2*5,280 feet; D is distance of highway right and 5280 is one mile in feet...I dont understand why are you combining these two things?

I understand this word problem like this:
L = 2 lanes;
d = 1/2x
s = 40 miles per hour.
no ?
Math Expert
Joined: 02 Sep 2009
Posts: 50002
Re: At a certain instant in time, the number of cars, N  [#permalink]

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11 Nov 2017, 09:29
dave13 wrote:
Bunuel wrote:
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

$$N=\frac{20Ld}{600+s^2}$$

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 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)

(A) 155
(B) 96
(C) 80
(D) 48
(E) 2

Given:
L = 2 lanes;
d = 1/2*5,280 feet;
s = 40 miles per hour.

Thus, $$N=\frac{20*2*\frac{1}{2}*5,280}{600+40^2}=48$$.

Bunuel hello, one question; Why did you write so d = 1/2*5,280 feet; D is distance of highway right and 5280 is one mile in feet...I dont understand why are you combining these two things?

I understand this word problem like this:
L = 2 lanes;
d = 1/2x
s = 40 miles per hour.
no ?

d is the length of the portion of the highway, in feet.

1/2-mile = 1/2*5,280 feet.
_________________
Re: At a certain instant in time, the number of cars, N &nbs [#permalink] 11 Nov 2017, 09:29

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