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M07-11 - GMAT club test

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M07-11 - GMAT club test [#permalink] New post 11 Sep 2012, 18:48
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A train traveling at a certain constant speed takes 30 seconds longer to travel 2 kilometers than it would take to travel 4 kilometers at 120 kilometers per hour. At what speed, in kilometers per hour, is the train traveling?
a) 40
b)48
c)80
d)96
e) 120

There is some problem with my understanding of this problem and the way it is solved in official answer. This is what I understood from the problem:
A train covers 4 kms @120kmph in certain time T secs.
Now, how much is the speed (in Kmph) of the train it it covers 2 Kms in (T + 30)secs?

If this understanding is correct then the answer is b) 48. But as per the official solution the answer is c) 80. I think as per my understanding b) is correct but the question is: Is my understanding correct? And if not then what does the question really means?
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Re: M07-11 - GMAT club test [#permalink] New post 11 Sep 2012, 19:34
akashv wrote:
A train traveling at a certain constant speed takes 30 seconds longer to travel 2 kilometers than it would take to travel 4 kilometers at 120 kilometers per hour. At what speed, in kilometers per hour, is the train traveling?
a) 40
b)48
c)80
d)96
e) 120

There is some problem with my understanding of this problem and the way it is solved in official answer. This is what I understood from the problem:
A train covers 4 kms @120kmph in certain time T secs.
Now, how much is the speed (in Kmph) of the train it it covers 2 Kms in (T + 30)secs?

If this understanding is correct then the answer is b) 48. But as per the official solution the answer is c) 80. I think as per my understanding b) is correct but the question is: Is my understanding correct? And if not then what does the question really means?


I interpreted the question exactly what you've described above. Hence, I think, your understanding is correct.
4 kms @120kmph = 120sec
Train time = 120+30 sec. Hence, 2 km in 150sec = 48Km/hr.

Can you post the OE?

Cheers!
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Re: M07-11 - GMAT club test [#permalink] New post 11 Sep 2012, 21:09
I too got the answer as 48 km/hr. here is how:

Let the speed be x km/hr. Equating the times in km/hr we get
\frac{2}{x} = \frac{4}{120} + \frac{30}{3600}
\frac{2}{x} = \frac{1}{24}
x= 48

IMO, for the OA to be true the question should read "30 seconds less to travel 2 kilometers" OR "2km at 120km/hr" unless I am missing something.
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Re: M07-11 - GMAT club test [#permalink] New post 12 Sep 2012, 01:32
Expert's post
akashv wrote:
A train traveling at a certain constant speed takes 30 seconds longer to travel 2 kilometers than it would take to travel 4 kilometers at 120 kilometers per hour. At what speed, in kilometers per hour, is the train traveling?
a) 40
b)48
c)80
d)96
e) 120

There is some problem with my understanding of this problem and the way it is solved in official answer. This is what I understood from the problem:
A train covers 4 kms @120kmph in certain time T secs.
Now, how much is the speed (in Kmph) of the train it it covers 2 Kms in (T + 30)secs?

If this understanding is correct then the answer is b) 48. But as per the official solution the answer is c) 80. I think as per my understanding b) is correct but the question is: Is my understanding correct? And if not then what does the question really means?


Edited the question. Thank you. +1.
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Re: M07-11 - GMAT club test   [#permalink] 12 Sep 2012, 01:32
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