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# Trains A and B which were originally 420 miles apart began traveling

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Math Expert
Joined: 02 Sep 2009
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Trains A and B which were originally 420 miles apart began traveling  [#permalink]

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12 Oct 2017, 05:04
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Difficulty:

45% (medium)

Question Stats:

63% (01:26) correct 37% (01:31) wrong based on 217 sessions

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Trains A and B which were originally 420 miles apart began traveling towards one another on parallel adjacent tracks. How many miles from the point where train A began to travel will the trains meet?

(1) Train A is traveling at a constant speed of 94 miles per hour and train B is traveling at a constant speed of 47 miles per hour.

(2) Train A is traveling at a constant speed that is twice the constant speed of train B.

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Re: Trains A and B which were originally 420 miles apart began traveling  [#permalink]

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12 Oct 2017, 05:34
1
D

St1
Let x be the required distance. Train A travels x distance and train B travels 420-x distance. Equating both as they start at the same time
X= 280 mile

St2
It’s same as st1 except that the speed is twice. So the same value of x can be calculated

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Re: Trains A and B which were originally 420 miles apart began traveling  [#permalink]

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12 Oct 2017, 06:31
1
Bunuel wrote:
Trains A and B which were originally 420 miles apart began traveling towards one another on parallel adjacent tracks. How many miles from the point where train A began to travel will the trains meet?

(1) Train A is traveling at a constant speed of 94 miles per hour and train B is traveling at a constant speed of 47 miles per hour.

(2) Train A is traveling at a constant speed that is twice the constant speed of train B.

(1) Distance = 420 miles

Speed A = 94
Speed B = 47

Relative Speed = 141 miles/hour
Time taken to meet = 420/141 = ~3 hrs
Distance travelled by Train A = 94*3 = 282 i.e. 2/3 part of the journey
Sufficient

(2) Since Distance to be travelled = 420 miles
Speed of Train A = 2* Speed of Train B
Distance travelled by Train A = 2 * Distance Travelled by Train B
Sufficient

D
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Re: Trains A and B which were originally 420 miles apart began traveling  [#permalink]

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12 Oct 2017, 06:52
Distance between the trains = 420 miles

Considering the trains start at the same time, they would have traveled for the equal amount of time before they meet.
So, Ta = Tb
(I) Da/Sa = Db/Sb
D = Distance traveled by single train
S = Speed of the single train

and from the question, (II) Da + Db = 420

We have a relation between Da and Db in (II). If we can eliminate Sa and Sb from (I), we will have two linear equations and we can solve for Da, which is being asked here.

Option 1. Sa = 94 mph; Sb = 47 mph; Sufficient
Option 2. Sa = 2s; Sb = s; Plug in these values in (I). Sufficient

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Re: Trains A and B which were originally 420 miles apart began traveling  [#permalink]

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18 Oct 2017, 03:30
Bunuel wrote:
Trains A and B which were originally 420 miles apart began traveling towards one another on parallel adjacent tracks. How many miles from the point where train A began to travel will the trains meet?

(1) Train A is traveling at a constant speed of 94 miles per hour and train B is traveling at a constant speed of 47 miles per hour.

(2) Train A is traveling at a constant speed that is twice the constant speed of train B.

D for me .. 1 and 2 st. basically state the same thing
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Re: Trains A and B which were originally 420 miles apart began traveling  [#permalink]

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23 Oct 2018, 20:41
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Re: Trains A and B which were originally 420 miles apart began traveling   [#permalink] 23 Oct 2018, 20:41
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