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The amount of coal a train burns each mile is directly propo

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The amount of coal a train burns each mile is directly propo  [#permalink]

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New post Updated on: 26 May 2014, 02:11
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The amount of coal a train burns each mile is directly proportional to the speed at which it travels. How much coal will it burn on this particular 60 mile trip?

(1) On a previous trip, the train burned 100 pounds of coal on a 60 mile trip at 60 miles per hour
(2) On this particular trip, the train is travelling at a speed of 30 miles per hour.


(isn't the second statement irrelevant? because once you know the value of the constant of fuel burned per speed (directly proportional to one another so it doesnt change in value), you know the distance, and since rate and time are inversely proportional to one another, doesn't the actual rate become unimportant? The book answer to this question was C, but I don't understand why its not A...)

Originally posted by gmatmathguy123 on 04 May 2010, 06:13.
Last edited by Bunuel on 26 May 2014, 02:11, edited 2 times in total.
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New post 04 May 2010, 07:29
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gmatmathguy123 wrote:
The amount of coal a train burns each mile is directly proportional to the speed at which it travels. How much coal will it burn on this particular 60 mile trip?
(1) On a previous trip, the train burned 100 pounds of coal on a 60 mile trip at 60 mph
(2) On this particular trip, the train is traveling at a speed of 30mph



(isn't the second statement irrelevant? because once you know the value of the constant of fuel burned per speed (directly proportional to one another so it doesnt change in value), you know the distance, and since rate and time are inversely proportional to one another, doesn't the actual rate become unimportant? The book answer to this question was C, but I don't understand why its not A...)


Given C = k*M, where C is amount of coal/per mile, k proportionality constant, and M speed of the train.
So, We have to find C and distance is given as 60
To find C, we need the value of k and the speed at which present journey is made.

Statement 1:
(100/60) = k*(60).. So k is 1/36, (Old journey..!!)
Now we have k..
DO we know the value of speed during the present journey..NO. INSUFFICIENT

Statement 2:
C = k* (60/30)
We have the speed of the present journey. But don't have the value of K.INSUFFICIENT

Statement 2 and Statement 1:
For present journey, we have K and the speed.. Answer C.
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New post 16 May 2010, 12:51
since the amount of coal the train burns is directly proportional to speed so the train burns a diffrent total amount of coal on the journey, more speed more amout of coal would be burnt, to get the fixed amount there must be a fixed speed which is provided by statement B , hence C is the right answer.
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Re: DS question...  [#permalink]

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New post 17 May 2010, 22:31
The amount of coal a train burns each mile is directly proportional to the speed at which it travels. How much coal will it burn on this particular 60 mile trip?
(1) On a previous trip, the train burned 100 pounds of coal on a 60 mile trip at 60 mph
(2) On this particular trip, the train is traveling at a speed of 30mph


We must know the speed of the train on this particular 60 mile trip. Second statement provides speed of 30mph.
Furthermore, We must know the constant associated with the proportion. Obviously, first statement helps to find the constant.
Therefore, We need both of the statements to answer the question.
Hence, answer is C
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Re: The amount of coal a train burns each mile is directly propo  [#permalink]

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New post 03 Jun 2014, 09:24
To answer the question we require to know the value of 2 parameters
1. Speed of the train
2. Rate of consumption of the coal.

From Option(1) we can only get rate of consumption of the coal. Speed of the train is unknown. Hence INSUFFICIENT
From Option(2) We only have the speed of the train. rate of consumption of coal is Unkown. Again INSUFFICIENT

Combining (1) and(2) we clearly get both the parameters

Hope This Helps
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New post 18 Jul 2016, 00:32
Sindbad wrote:
To answer the question we require to know the value of 2 parameters
1. Speed of the train
2. Rate of consumption of the coal.

From Option(1) we can only get rate of consumption of the coal. Speed of the train is unknown. Hence INSUFFICIENT
From Option(2) We only have the speed of the train. rate of consumption of coal is Unkown. Again INSUFFICIENT

Combining (1) and(2) we clearly get both the parameters

Hope This Helps

People implied here that => if y is proportional to x, it means y = mx .
But its actually y = mx +c . Here is the special case since if speed is 0, we are taking special condition and saying fuel consumed will be 0.
If it was anything other than speed and coal consumption question, i think that time answer should have been E.
But i am not sure of that also.. :( Can anyone please confirm it ??
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