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Data Sufficiency Question

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by Ankush2008 » Sat Aug 02, 2008 1:48 pm
Two trains P and Q are running on parallel tracks in opposite directions. The trains started 250 miles apart and cross each other in exactly 2 hours. Does train T cover more distance than train Q in 2 hours.

1. Train P averaged a speed of 70 miles/hr.
2. Train Q averaged a speed of 55 miles/hr.

(A) Statement 1 is sufficient in itself
(B) Statement 2 is sufficient in itself
(C) Statement 1 and 2 taken together are sufficient.
(D) Both are sufficient by themselves.
(E) Both statements are insufficient.
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by parallel_chase » Sat Aug 02, 2008 3:11 pm
I think the answer is D.

From the question stem you find that the increasing or decreasing speed between the trains is 250/2=125mph,

Therefore,
P's speed + Q's speed =125

We just have to find the speed of each train. The faster train will take less time and cover more distance.

Statement I

P's speed= 70mph

70+Q=125 => Q=55
Sufficient.

Statement II

P+55 =125 => P=70
Sufficient.

Hence D is the answer.

Let me know if you still have any doubts.
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by Vignesh.4384 » Sat Aug 02, 2008 9:25 pm
IMO D
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by Dagdoo » Sun Aug 03, 2008 9:54 am
Hi Paralle_chase,

I am not able to understand your statement "From the question stem you find that the increasing or decreasing speed between the trains is 250/2=125mph" I am not able to understand it. So can you please explain?
parallel_chase wrote:I think the answer is D.

From the question stem you find that the increasing or decreasing speed between the trains is 250/2=125mph,

Therefore,
P's speed + Q's speed =125

We just have to find the speed of each train. The faster train will take less time and cover more distance.

Statement I
P's speed= 70mph

70+Q=125 => Q=55
Sufficient.

Statement II

P+55 =125 => P=70
Sufficient.

Hence D is the answer.

Let me know if you still have any doubts.
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by parallel_chase » Sun Aug 03, 2008 11:02 am
If two trains are traveling in opposite direction you add the speeds of both the trains to find the increasing or decreasing speed.

If two trains are 250 miles apart and they pass each in exactly two hours.

The increasing or decreasing speed = D/T =250/2 =125

If the two trains were traveling in the same direction then you would subtract the speeds of both the trains.

The speed is increasing or decreasing because when the trains traveling in opposite direction the distance is decreasing between them but when the two trains have passed each other the distance is actually increasing.

Hope this helps, let me know if you still have any doubts.
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