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# Stations X and Y are connected by two straight parallell

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Stations X and Y are connected by two straight parallell [#permalink]  20 May 2005, 21:05
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Stations X and Y are connected by two straight parallell lines that are 250 miles long.Train P and train Q start at the same time from station X and Y respectively and each train travelled toward other train's point of departure..the two trains passed each other after travelling for 2 hours.when the two trains passed which of the two trains was nearer to the destination ?

(1) At the time when the two trains passed, the train P maintained an average speed of 70 miles/hour

(2) Train Q averaged 55miles/hr for the entire trip
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sparky wrote:
E.

From the question stem ,we can conclude the sum of the average speeds is 125 m/h.

A [insufficient]doesn't help us with the speed of either of the trains ( speed at the point of meeting is no good)

B[sufficient] - Q averages 55 m/h , i.e P averages 70 m/h. So P is nearer to it's destination.

Hence B

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B[sufficient] - Q averages 55 m/h , i.e P averages 70 m/h. So P is nearer to it's destination.

did not you borrow this info from the 1st statement? and then the answer should be C.

can you use P's speed (70) for the average speed? i guess if you can, then it's C. and if you can't then it's E
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pb_india wrote:
What's wrong with A?

A would not suffice as the question doesn't mention that the trains maintained a steady speed throughout the journey, henc it is possible that the train accelerated to 70 m/h just when it was about to pass the other train, hence we are inconclusive about the speeds.

Hope this helps.

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Re: DS - Trains [#permalink]  21 May 2005, 20:06
pb_india wrote:
Stations X and Y are connected by two straight parallell lines that are 250 miles long.Train P and train Q start at the same time from station X and Y respectively and each train travelled toward other train's point of departure..the two trains passed each other after travelling for 2 hours.when the two trains passed which of the two trains was nearer to the destination ?

(1) At the time when the two trains passed, the train P maintained an average speed of 70 miles/hour

(2) Train Q averaged 55miles/hr for the entire trip

B alone is not sufficient. average speed for the entire trip is 55miles/hr. it means speed could have been minimal in first two hours and very high the rest of the time.
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I think the 70 mph average speed of train A at the time of passing means its distance over time it took from the start to the meeting point. So P travelled 140 miles in the first two hours. Hence this is sufficient. I don't think you never define average speed at a point, you only define average speed over certain time or distance.

On the other hand, Q's speed of 55 mph over the entire route is a little shady since the speed in the first 2 hrs can be lower or higher than this (and hence the distance also). So, this is not sufficient.

So I go with A.
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Re: DS - Trains [#permalink]  21 May 2005, 21:30
(1) At the time when the two trains passed, the train P maintained an average speed of 70 miles/hour

We know the average speed for P and the time P has travelled (2hr) from the stem. We can then derive how much has P travelled and how far it is from its distant. We can then also know where Q is at the time when they meet. So a comparison is possible. Sufficient.

(2) Train Q averaged 55miles/hr for the entire trip
Average speed for the entire trip doesn't help, since Q could be travelling much faster before they meet, and then slower after they meet. Or the other way around. There's not sufficient info for us to determine the distance Q travelled when they meet.
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Old discussion thread is located here.

http://www.gmatclub.com/phpbb/viewtopic.php?t=13403
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Definitely D, as each option states can be used to calculate the speed for the other train, from which we can find out the remaining distance towards destinnation.

Total Distance = TS1 + TS2
250 = T(S1+S2), where T = 2
Therefore, 125 = T1 + T2

(A). T1 = 70 -> T2 = 55 -> Train A is near to destination
(B). T2 = 55 -> T1 = 70 -> Train A is near to destination

Hence, D
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amit_drummer wrote:
Definitely D, as each option states can be used to calculate the speed for the other train, from which we can find out the remaining distance towards destinnation.

Total Distance = TS1 + TS2
250 = T(S1+S2), where T = 2
Therefore, 125 = T1 + T2

(A). T1 = 70 -> T2 = 55 -> Train A is near to destination
(B). T2 = 55 -> T1 = 70 -> Train A is near to destination

Hence, D

Convinced beyond doubt it is A.

amitdrummer, your soln would work only in S1 and S2 represent average speeds of the trains at the time of crossing over (after all we are not bother about what happened after they crossed over, and average speed of the entire journey is not related to the av. speed at the time of crossing over).

Hope this helps.

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Out of 2 big discussions no OA is posted. Is this a real question off of a real GMAT test, or a made up question? If it's real, please post the OA.

Thanks.
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Of course,it is real GAMT question.See the old discussoinHongHu posted.

From the link ,OA is A.

"Averaged entire trip" was the trap for me.It sounds as if constant speed was maintained for the entire trip,but it was the average.
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an honghu mentioned....A it is...
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pb_india,

Where did this question come from? Was it on an actual GMAT test?

Thanks.
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