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Manager  Joined: 08 Nov 2008
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Stations X and Y are connected by two separate, straight, parallel  [#permalink]

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Question Stats: 42% (01:47) correct 58% (01:53) wrong based on 988 sessions

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Stations X and Y are connected by two separate, straight, parallel rail lines that are 250 miles long. Train P and train Q simultaneously left Station X and Station Y, respectively, and each train traveled to the other’s point of departure. The two trains passed each other after traveling for 2 hours. When the two trains passed, which train was nearer to its destination?

(1) At the time when the two trains passed, train P had averaged a speed of 70 miles per hour.
(2) Train Q averaged a speed of 55 miles per hour for the entire trip.

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Re: Stations X and Y are connected by two separate, straight, parallel  [#permalink]

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Stations X and Y are connected by two separate, straight, parallel rail lines that are 250 miles long. Train P and train Q simultaneously left Station X and Station Y, respectively, and each train traveled to the other’s point of departure. The two trains passed each other after traveling for 2 hours. When the two trains passed, which train was nearer to its destination?
(1) At the time when the two trains passed, train P had averaged a speed of 70 miles per hour.
(2) Train Q averaged a speed of 55 miles per hour for the entire trip.

(1) As P averaged 70 miles per hour at the time when the two trains passed, hence when they passed each other P traveled 2*70=140 miles, so for P it was 110 miles left to cover and for Q 140. P was closer to its destination. Sufficient.

(2) Knowing average speed for entire trip won't help us to determine the distance either of train coverd at the time they passed each other (as the average speed at the time the met could have been different). Not sufficient.

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Re: Stations X and Y are connected by two separate, straight, parallel  [#permalink]

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Stations X and Y are connected by two separate, straight, parallel rail lines that are 250 miles long. Train P and train Q simultaneously left Station X and Station Y, respectively, and each train traveled to the other’s point of departure. The two trains passed each other after traveling for 2 hours. When the two trains passed, which train was nearer to its destination?

(1) At the time when the two trains passed, train P had averaged a speed of 70 miles per hour.
(2) Train Q averaged a speed of 55 miles per hour for the entire trip

SOLUTION:

D = 250 miles
P and Q travel 2 hrs each before they meet

From (1): P speed = 70 mph i.e. in 2 hrs it covers 140 miles
Therefore, Q must have traveled = 110 miles ---- SUFFICIENT

From (2): Q speed for ENTIRE trip = 55 mph ---- Clearly INSUFFICIENT

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GMAT 1: 750 Q49 V43 Re: Stations X and Y are connected by two separate, straight, parallel  [#permalink]

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Stations X and Y are connected by two separate, straight, parallel rail lines that are 250 miles long. Train P and train Q simultaneously left Station X and Station Y, respectively, and each train traveled to the other’s point of departure. The two trains passed each other after traveling for 2 hours. When the two trains passed, which train was nearer to its destination?

(1) At the time when the two trains passed, train P had averaged a speed of 70 miles per hour.
Train P has been running for 2 hours with an average speed of 70 miles per hour so it has covered 140 km .
The total distance is 250; so P was 250-140= 90 miles away from its destination .
We can use logic to see that since the train are crossing each other then train Q must also travelled 90 kilometres and thus it was 250-90 = 160 km away from its destination
Train P was closer
SUFFICIENT

(2) Train Q averaged a speed of 55 miles per hour for the entire trip.
Well the speed for first hour can vary from the second's hour's speed and so on.
We don know at what speed train Q travelled for the first 2 hours so we cannot figure out its distance.
INSUFFICIENT

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Re: Stations X and Y are connected by two separate, straight, parallel  [#permalink]

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Sorry but the explanation for statement 1 is not clear from the above thread. Can someone please explain how do we know the speed of Q and how do we derive that equation. Thank you.
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Re: Stations X and Y are connected by two separate, straight, parallel  [#permalink]

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longhaul123 wrote:
Sorry but the explanation for statement 1 is not clear from the above thread. Can someone please explain how do we know the speed of Q and how do we derive that equation. Thank you.

X------(140 miles)--------(meeting point)------(110 miles)-----Y
P -->..........................................................................<--Q

Trains meet after 2 hours. Train P's rate was 70 miles per hour at the time when the two trains met, hence P traveled 2*70=140 miles. Thus Q traveled 250 - 140 = 110 miles. We don't need the rate of Q to answer the question but we can get it. It would be (distance traveled)/(time) = 110/2 = 55 miles per hour.
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Re: Stations X and Y are connected by two separate, straight, parallel  [#permalink]

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Bunuel wrote:
udaymathapati wrote:
Stations X and Y are connected by two separate, straight, parallel rail lines that are 250 miles long. Train P and train Q simultaneously left Station X and Station Y, respectively, and each train traveled to the other’s point of departure. The two trains passed each other after traveling for 2 hours. When the two trains passed, which train was nearer to its destination?
(1) At the time when the two trains passed, train P had averaged a speed of 70 miles per hour.
(2) Train Q averaged a speed of 55 miles per hour for the entire trip.

Straight A, the asnwer cannot be C.

(1) As P averaged 70 miles per hour at the time when the two trains passed, hence whey they passed each other P traveled 2*70=140 miles, so for P it was 110 miles left to cover and for Q 140. P was closer to its destination. Sufficient.

(2) Knowing average speed for entire trip won' help us to determine the distance either of train covered at the time they passed each other (as the average speed at the time the met could have been different). Not sufficient.

Bunuel
I did not understand still that even if option 1 gives us P is 110 miles away from destination how can we conclude that P is nearer at that time without knowing anything about Q?
If we are to compare P & Q's distance from the destination when they pass each other, we need to know Q's distance too at that time right?
Thanks!
Math Expert V
Joined: 02 Sep 2009
Posts: 58427
Re: Stations X and Y are connected by two separate, straight, parallel  [#permalink]

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1
Shenaz wrote:
Bunuel wrote:
udaymathapati wrote:
Stations X and Y are connected by two separate, straight, parallel rail lines that are 250 miles long. Train P and train Q simultaneously left Station X and Station Y, respectively, and each train traveled to the other’s point of departure. The two trains passed each other after traveling for 2 hours. When the two trains passed, which train was nearer to its destination?
(1) At the time when the two trains passed, train P had averaged a speed of 70 miles per hour.
(2) Train Q averaged a speed of 55 miles per hour for the entire trip.

Straight A, the asnwer cannot be C.

(1) As P averaged 70 miles per hour at the time when the two trains passed, hence whey they passed each other P traveled 2*70=140 miles, so for P it was 110 miles left to cover and for Q 140. P was closer to its destination. Sufficient.

(2) Knowing average speed for entire trip won' help us to determine the distance either of train covered at the time they passed each other (as the average speed at the time the met could have been different). Not sufficient.

Bunuel
I did not understand still that even if option 1 gives us P is 110 miles away from destination how can we conclude that P is nearer at that time without knowing anything about Q?
If we are to compare P & Q's distance from the destination when they pass each other, we need to know Q's distance too at that time right?
Thanks!

P is 110 miles from the destination at the moment when P and Q meet. Since the whole distance is 250 miles, then Q is 250 - 110 = 140 miles from the destination.
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Re: Stations X and Y are connected by two separate, straight, parallel  [#permalink]

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_________________ Re: Stations X and Y are connected by two separate, straight, parallel   [#permalink] 02 Oct 2019, 03:51
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