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.