In solution authors use miles per hour to represent speed, but feet to represent distance.
Shouldn't we first choose one measurement? e.g. use only feet both for speed and distance or only miles for speed and distance.
Can we divide feet by miles? I always thought that no.
Could anybody please clarify this particular problem for me.
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13th edition. Problem solving, â„– 70
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Olga Lapina
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ganeshrkamath
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You're right. It is a recommended practice to convert the units to one system.Olga Lapina wrote:In solution authors use miles per hour to represent speed, but feet to represent distance.
Shouldn't we first choose one measurement? e.g. use only feet both for speed and distance or only miles for speed and distance.
Can we divide feet by miles? I always thought that no.
Could anybody please clarify this particular problem for me.
But, in this problem, the formula specifically says what units are to be used for the individual factors. So you have to use those same units to arrive at the solution.
Hope this helps.
Cheers
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The prompt instructs us to estimate the value of n BASED ON THE FORMULA.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 = (20Ld)/(600+ s²)
where:
L is the number of lanes in the same direction,
d is the length of the portion of the highway, in FEET
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) 24
In the formula:
d is in terms of FEET.
s in in terms of MILES per hour.
Thus, we must plug the following values into the formula:
L=2. (Since there are 2 lanes.)
d=2640 (Since 1/2 mile = 2640 feet.)
s=40. (Since the average speed is 40 miles per hour.)
Result:
N =
= (20*2*2640)/(600 + 40²)
= (20*2*2640)/(600 + 1600)
= (2*2*264)/(6+16)
= (2*2*264)/22
= (2*2*12)
= 48.
The correct answer is D.
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Olga Lapina
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