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Re: John and Karen begin running at opposite ends of a trail unt [#permalink]
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Kinshook wrote:
Narenn wrote:
A Nice Question from VERITAS.
OA and OE will be posted after few responses. Brief and Correct explanations will be rewarded with a Kudo.



John and Karen begin running at opposite ends of a trail until they meet somewhere in between their starting points. They each run at their respective constant rates until John gets a cramp and stops. If Karen runs 50% faster than John, who is only able to cover 25% of the distance before he stops, what percent longer would Karen have run than she would have had John been able to maintain his constant rate until they met.

A) 25%
B) 50%
C) 75%
D) 100%
E) 200%

Happy Solving!


Given:
1. John and Karen begin running at opposite ends of a trail until they meet somewhere in between their starting points.
2. They each run at their respective constant rates until John gets a cramp and stops.

Asked: If Karen runs 50% faster than John, who is only able to cover 25% of the distance before he stops, what percent longer would Karen have run than she would have had John been able to maintain his constant rate until they met.

vK / vJ = 1.5

Let the speeds of John and Karen be 2x & 3x mph respectively

Let the length of the trail be L miles

Normal Case:
Distance = L miles
Relative speed = 2x + 3x = 5x mph
Time taken to meet = L/5x= .2L/x hours

Abnormal Case : John is only able to cover 25% of the distance before he stops
Time when both were running = (L/4)/5x = L/20x hours
Distance covered by both in L/20x hours = L/20x * (2x + 3x) = L/4

Remaining distance = 3L/4
Time taken by Karen to cover 3L/4 distance = 3L/4 /(3x) = L/4x

Total time run by Karen = L/20x + L/4x = 6L/20x = 3L/10x = .3L/x

Extra time run by Karen = .3L/x - .2L/x = .1L/x

Percent longer would Karen have run ={ (.1L/x)/(.2L/x)}*100% = 50%

IMO B

Bunuel
I think OA should be B
Please check whether OA is correct.


Yes I thought the answer would be 50% too. Assuming the total distance to be 180km, in the normal scenario, Karen would have traveled 108km while John would have traveled 72km when they would have met. So I assumed that John had traveled only 25% of his estimated distance and not the overall. This would've led to Karen having to travel an additional 54km, thereby leading to a 50% increase in time.

Bunuel, chetan2u, Narenn, is the wording of the question ambiguous or have I misinterpreted it?

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Re: John and Karen begin running at opposite ends of a trail unt [#permalink]
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Expert Reply
Narenn wrote:
A Nice Question from VERITAS.
OA and OE will be posted after few responses. Brief and Correct explanations will be rewarded with a Kudo.



John and Karen begin running at opposite ends of a trail until they meet somewhere in between their starting points. They each run at their respective constant rates until John gets a cramp and stops. If Karen runs 50% faster than John, who is only able to cover 25% of the distance before he stops, what percent longer would Karen have run than she would have had John been able to maintain his constant rate until they met.

A) 25%
B) 50%
C) 75%
D) 100%
E) 200%



Let’s assume that John runs at 10 mi/hr, and thus, Karen runs at 10 x 1.5 = 15 mi/hour. If we assume that the distance between them was 100 miles, then when John stopped, he had run 25 miles and Karen had to run 75 miles to meet him, and thus her running time was 75 / 15 = 5 hours.

Had John not stopped, they would have met when he had run 40 miles and she had run 60 miles (ratio of 10 : 15); thus, her running time would have been 60 / 15 = 4 hours.

The percent longer that Karen would have had to run is (50 - 40) / 40 x 100% = 25%.

Answer: A

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Re: John and Karen begin running at opposite ends of a trail unt [#permalink]
Hello Bunuel,

I have a confusion. "Covering 25% of the distance" could mean 2 things:
1. covered 25% of the total length of the track.
2. covered 25% of the distance he was originally supposed to cover.

How do we decide between the two? Shouldn't the wording of the question be made more clear?
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Re: John and Karen begin running at opposite ends of a trail unt [#permalink]
Karen has 1,5*velocity of Jhon.

Then, we can state that Karen runs 3/5 of the distance and Jhon runs 2/5 of the distance.

If Jhon gets injured after running 1/4 of the total distance, Karen has to run 2/5 - 1/4 = 3/20 more.

Which corresponds to + (3/20)/(3/5) = +25% over the distance she used to run.
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Re: John and Karen begin running at opposite ends of a trail unt [#permalink]
Is "only able to cover 25% of the distance before he stops" a tad bit ambiguous?

Say the track length is 100ft

Normally J = 40ft, K = 60ft

If J gets cramps after 25% of the total distance (how the answer is structured), J gets cramps after 25ft, and K has to run 75ft, 75/60 = 25%

If J gets cramps of 25% of his normal responsibility (completely reasonable interpretation of the question how currently worded), J runs 10ft and K runs 90ft, 90/60 = 50%, which also is an answer.

Would a GMAT question be this unclear?
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Re: John and Karen begin running at opposite ends of a trail unt [#permalink]
This would make more sense with the following change:

If Karen runs 50% faster than John, who is only able to cover 25% of the distance before he stops, what percent longer did Karen run than she would have had John been able to maintain his constant rate until they met.

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