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DS - time speed

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30 Aug 2004, 09:12
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Can anyone explain what the first stem means.
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Manager
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30 Aug 2004, 09:55
The first stem basically means, X crossed Y for the second time. This stem does not indicate anything about TIMES, hence is insufficient.

The answer to this problem would be B.

Total miles = 10,000
Track size = 400
No. of laps = 10,000 / 400 = 25

Now X takes 60 seconds/lap, for the whole race (25 laps) = 25 x 60
Now Y takes 62.4 seconds/lap, for the whole race (25 laps) = 25 x 62.4

Total race time for X : Total race time for Y
=> (25 x 60) / (25 x 62.4) = 25/26
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30 Aug 2004, 10:12
A is insufficient.

My choice is B
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30 Aug 2004, 10:17
I would choose B too.

St.1 doesnt indicate anything about the time for X and Y
St.2 gives us the average of both x and y, while we know they both had to run 25 laps.

Regards,

Alex
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30 Aug 2004, 10:20
The first stem means that the first runner crossed the second two times. The net distance between them is therefore 400x2=800.
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30 Aug 2004, 11:20
assuming average times over the race, doesn't A) indicate that X was two laps ahead of Y? thus, meaning that X had finished 10,000 meters, whereas Y had only finished 9,200 meters? so isn't the ratio of time the same as the ratio of distance? thus the ratio of Y to X was 9200 to 10000, or 23/25?
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30 Aug 2004, 15:33
well, we know that while X (first runner) completed 25 laps, Y (second runner) completed 23 laps. Hence, in the same time, one completed 10,000, while the other completed 9,200. I think, we can pick any time for T here and get the relationship of t1 to t2.
hence I'd go for D
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30 Aug 2004, 22:49
I'll deal with the simple one first.

From the question, we know they need to do 10,000/400=25 laps

From (2), X takes 60*25 = 1500 seconds, and Y takes 62.4*25 = 1560 seconds
With this in hand, (2) is sufficient.

Now we need to consider (1).
When X finishes 25 laps, he lapped Y for the second time. This means he is 800 meters ahead.
All we have is information about the distance X and Y have already ran, but nothing about their speed, and so we can conclude the time they took and hence the ratio of their time.
Therefore (1) is not sufficient.

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31 Aug 2004, 00:22
The OA is B.
I couldn't understand what A means exactly. Thanks guys for explaining the meaning.
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01 Sep 2004, 06:48
I think what is tricky whith statement 1 is that we do not know how much time will need Y to complete the 2 remaining laps after he was crossed by X.

I would also choose B
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01 Sep 2004, 07:57
twixt wrote:
I think what is tricky whith statement 1 is that we do not know how much time will need Y to complete the 2 remaining laps after he was crossed by X.

I would also choose B

Wow! I choose D considering that Y travels at a constant speed. Good catch.

Just for discussion, If the question is:
Two Runners, X and Y, competed in a 10000 m run. The race took place in a oval track 400m long. What is tha ration od X's time to Y's time, if they run at constant speed?
(1) Just a X crossed the finish line, he lapped Y for the second time.
(2) X averaged 60s per lap, and Y averaged 62.4 s per lap.

01 Sep 2004, 07:57
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DS - time speed

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