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A train traveled from Station A to Station B at an average speed of 80

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A train traveled from Station A to Station B at an average speed of 80 [#permalink] New post 04 Jun 2014, 23:00
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A train traveled from Station A to Station B at an average speed of 80 kilometers per hour and then from Station B to Station C at an average speed of 60 kilometers per hour. If the train did not stop at Station B, what was the average speed at which the train traveled from Station A to C?

(1) The distance that the train traveled from Station A to Station B was 4 times the distance that train traveled from Station B to Station C.
(2) The amount of time it took to the train to travel from Station A to Station B is 3 times the amount of time that it took the train to travel from Station B to Station C.

[Reveal] Spoiler:
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Screen_Shot_2012_05_15_at_8_48_47_PM.png
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[Reveal] Spoiler: OA

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Last edited by Bunuel on 08 Jun 2015, 01:59, edited 2 times in total.
Renamed the topic and edited the question.
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Re: A train traveled from Station A to Station B at an average speed of 80 [#permalink] New post 05 Jun 2014, 00:29
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MensaNumber wrote:
A train traveled from station A to station B at an average speed of 80 kmph and then from Station B to Station C at an average speed of 60 kmph. What was the average speed from A to C?

1. The distance from A to C four times the distance from B to C
2. The amount of time it took to travel from A to B is four time that of time it took to travel from B to C

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Average speed = total distance/ total time.

1) A-----B-------C

let bc=x, therefore AC=4x, and AB=3x

thus average speed = 4x/{(3x/80)+(x/60)}

we can easily calculate the value of avg. speed from the above exp. hence sufficient

2) A---------B----------c

let distance between AB=x and BC=y
x/80=4(y/60)

x=(16/3)y-------------1)

average speed = x+y/{(x/80)+(y/60)}

we can substitute the value of x in terms of y in the above expression to find out the average speed. hence sufficient

therefore correct answer should be D
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Re: A train traveled from Station A to Station B at an average speed of 80 [#permalink] New post 06 Jun 2015, 04:40
Is there a quicker way to see that the distance variable cancels out, rather than going through the entire algebraic calculation? I made the assumption that the variable would remain, and struggle to finish in ~ 2 minutes once I start getting into algebra for DS questions. Thanks..
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Re: A train traveled from Station A to Station B at an average speed of 80 [#permalink] New post 06 Jun 2015, 06:38
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ElCorazon wrote:
Is there a quicker way to see that the distance variable cancels out, rather than going through the entire algebraic calculation? I made the assumption that the variable would remain, and struggle to finish in ~ 2 minutes once I start getting into algebra for DS questions. Thanks..


Hi ElCorazon,
the Q stem tells us the speed in two different routes and asks us the average speed..
for this we require the distance or the ratio of distances..
lets see the statement..
1)statement 1 gives us the ratio of distance .. so sufficient..
2) statement two tells us the ratio of time so multiplying this ratio with speed would give us the ratio of distance .. again sufficient

ans D
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Re: A train traveled from Station A to Station B at an average speed of 80 [#permalink] New post 06 Jun 2015, 10:51
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Hi ElCorazon,

The 'goal' to try to answer each Quant question in under 2 minutes is NOT practical. While some questions can be solved relatively quickly (in under 30 seconds), certain questions are designed to take longer to solve (upwards of 3 minutes, and that's if you KNOW what you're doing). These types of "multi-step trip" questions are usually wordier, take more steps to solve and require a higher degree of organization and attention-to-detail than most prompts, so it's understandable that you would need MORE than 2 minutes to solve it.

Instead of having a "2 minutes or less" goal, focus more on your overall efficiency - you should try to get this question correct without wasting time.

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Re: A train traveled from Station A to Station B at an average speed of 80 [#permalink] New post 06 Jun 2015, 14:30
EMPOWERgmatRichC wrote:
Hi ElCorazon,

The 'goal' to try to answer each Quant question in under 2 minutes is NOT practical. While some questions can be solved relatively quickly (in under 30 seconds), certain questions are designed to take longer to solve (upwards of 3 minutes, and that's if you KNOW what you're doing). These types of "multi-step trip" questions are usually wordier, take more steps to solve and require a higher degree of organization and attention-to-detail than most prompts, so it's understandable that you would need MORE than 2 minutes to solve it.

Instead of having a "2 minutes or less" goal, focus more on your overall efficiency - you should try to get this question correct without wasting time.

GMAT assassins aren't born, they're made,
Rich

Hi Rich!
I watched EMPOWERGmat course and you said that if we have a ratios that means that statement is sufficient. Hence answer is D. Do i think logically?=))
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Re: A train traveled from Station A to Station B at an average speed of 80 [#permalink] New post 07 Jun 2015, 16:11
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This question is not correct, because the statements conflict each other. It is impossible that, given A to B is 80 mph and B to C is 60 mph, both of these statements could be true. Think about this example:

Statement 1 - assume distance from A to C is 320 miles. Because A to C is 4x B to C, then A to B is 3x B to C. Its a 3:1 ratio in the distances. Therefore we have 240 miles from A to B and 80 miles from B to C. That leaves us with time of 3 hours from A to B and time of 1 hour 20 minutes from B to C.

Statement 2- this can't be possible given what we just figured out in statement 1. 3:1.33 does not equal 3:1.

The question is flawed.
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Re: A train traveled from Station A to Station B at an average speed of 80 [#permalink] New post 08 Jun 2015, 02:01
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VeritasPrepBrandon wrote:
This question is not correct, because the statements conflict each other. It is impossible that, given A to B is 80 mph and B to C is 60 mph, both of these statements could be true. Think about this example:

Statement 1 - assume distance from A to C is 320 miles. Because A to C is 4x B to C, then A to B is 3x B to C. Its a 3:1 ratio in the distances. Therefore we have 240 miles from A to B and 80 miles from B to C. That leaves us with time of 3 hours from A to B and time of 1 hour 20 minutes from B to C.

Statement 2- this can't be possible given what we just figured out in statement 1. 3:1.33 does not equal 3:1.

The question is flawed.


Thank you for noticing this. Edited the question.
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Re: A train traveled from Station A to Station B at an average speed of 80   [#permalink] 08 Jun 2015, 02:01
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