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# At what speed was a train traveling on a trip when it had

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At what speed was a train traveling on a trip when it had [#permalink]

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13 Dec 2012, 05:52
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At what speed was a train traveling on a trip when it had completed half of the total distance of the trip?

(1) The trip was 460 miles long and took 4 hours to complete.
(2) The train traveled at an average rate of 115 miles per hour on the trip.
[Reveal] Spoiler: OA

Last edited by Bunuel on 21 Jul 2013, 11:32, edited 1 time in total.
Edited the OA.
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Re: At what speed was a train traveling on a trip when it had [#permalink]

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13 Dec 2012, 05:58
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At what speed was a train traveling on a trip when it had completed half of the total distance of the trip?

Notice that we are not told that the train travels at a constant speed.

(1) The trip was 460 miles long and took 4 hours to complete --> the average speed of the train was 460/4=115 miles per hour, but we don't know what was the speed of the train when it had completed half of the total distance (230 miles). Not sufficient.

(2) The train traveled at an average rate of 115 miles per hour on the trip. The same as above. Not sufficient.

(1)+(2) We only know that the average speed of the train was 115 miles per hour, which is not enough to determine the speed of the train when it had completed half of the total distance (230 miles). Not sufficient.

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Re: At what speed was a train traveling on a trip when it had [#permalink]

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17 Dec 2012, 11:57
why is the official answer D?
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Re: At what speed was a train traveling on a trip when it had [#permalink]

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25 Dec 2012, 05:20
The OA is E. It is given in the OG as well
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Re: At what speed was a train traveling on a trip when it had [#permalink]

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01 Aug 2013, 11:29
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At what speed was a train traveling on a trip when it had completed half of the total distance of the trip?

(1) The trip was 460 miles long and took 4 hours to complete.
The train could have been moving at a slower speed for the first part of the trip then faster for the second part to complete the journey in 4 hours.
INSUFFICIENT

(2) The train traveled at an average rate of 115 miles per hour on the trip.
We know nothing about distance and it's possible that the train was traveling at a slower rate for the first part of the trip then faster for the second part of the trip to average out to 115 MPH.
INSUFFICIENT

1+2)
There still is not enough information to solve for this problem. We know that the train averaged 115MPH and that it took four hours to complete the trip (i.e. it took 4 hours) but the train could have moved slower for the first portion of the trip and faster for the second portion of the trip. there is no way of knowing for sure.
INSUFFICIENT

(E)
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Re: At what speed was a train traveling on a trip when it had [#permalink]

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15 Sep 2014, 07:42
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Re: At what speed was a train traveling on a trip when it had [#permalink]

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28 Apr 2016, 06:50
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: At what speed was a train traveling on a trip when it had [#permalink]

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28 Apr 2016, 14:52
As we don't know whether the train is travelling at a constant speed,the answer is got to be E
Anyway for understanding here is a explaination
Statement 1 gives information about the total distance traveled in total time which will give us the average speed, but we can't deduce anything about the speed of the train when it had completed half of its distance, So insufficient

Statement 2 gives information about the average speed, but we can't deduce anything about the speed of the train when it had completed half of its distance, So insufficient
Combining both statements they are providing the same information
We only know that the average speed of the train was 115 miles per hour, which is not enough to determine the speed of the train when it had completed half of the total distance (230 miles) So insufficient
Correct Answer - E
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Re: At what speed was a train traveling on a trip when it had [#permalink]

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14 May 2016, 07:52
At what speed was a train traveling on a trip when it had completed half of the total distance of the trip?

(1) The trip was 460 miles long and took 4 hours to complete.
(2) The train traveled at an average rate of 115 miles per hour on the trip.

Solution:

We need to determine at what speed a train was traveling when it completed ½ of its trip.

Statement One Alone:

The trip was 460 miles long and took 4 hours to complete.

With the information in statement one, we can determine the average speed of the train for the entire trip.

average speed = total distance/total time

average speed = 460/4

average speed = 115

Although we know that the train traveled at an average speed of 115 mph, we do not know whether the train traveled at a constant rate. Thus, we cannot determine the speed of the train when it completed half of the total distance. Statement one alone is not sufficient to answer the question. We can eliminate answer choices A and D.

Statement Two Alone:

The train traveled at an average rate of 115 miles per hour on the trip.

We see that statement two provides the same information as statement one and thus is also not sufficient to answer the question. We can eliminate answer choice B.

Statements One and Two Together:

Since statements one and two provide identical information and are each insufficient, we know that the statements together are also insufficient.

The answer is E.
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At what speed was a train traveling on a trip when it had [#permalink]

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23 Sep 2016, 13:49
If you recall your physics class in high school you can solve this question in less than 30 seconds...

For starters: The question asks for the instantaneous speed of the train.

In this world there are ONLY two WAYs in order to be able to know the instantaneous speed of any object.

1) If someone tells you the speed @ that specific instance (lol)

2) If you have a speed equation with the unknown variable being the time, i.e. s(t) = function of speed ...
For example if we were in a position to derive from the given info an equation with 1 unknown like fore example..

Speed = 2t + 3
OR
Speed = a*t^2 + t + t/2 + c/g ETC ... OR any type of equation with a single variable t for time

then the only thing you need to do is replace the variable t with the time instance asked in the question and you are done. Although be very careful with the units of t.

This question doesn't do any of the two so you should be able to pick E very quickly.

Some might argue that the constant rate might cause a problem but hey this is nothing more than an equation with 0 unknown or in other words it will have the form y=b. Since we talk for speed and time for convenience Speed = α where α can be any value.

So if the question was saying that for a journey of Gazillion hours the speed of the train was constant at a m/s then you know that s = a which means that throughout the whole journey its speed was CONSTANT and never changed.
At what speed was a train traveling on a trip when it had   [#permalink] 23 Sep 2016, 13:49
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# At what speed was a train traveling on a trip when it had

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