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Source: — Problem Solving |
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by niksworth » Mon Sep 20, 2010 10:33 am
1 km = 1000 m

1 hr = 60 min = 60 x 60 sec = 3600 sec

y km / hr = y * (1000 m / 3600 sec) = y * (5 m / 18 sec)

But it is given in the question that

y km / hr = x m / sec
or, y * (5 / 18) m / sec = x m / sec
or, y * (5 / 18 ) = x
or, y = (18 / 5) x

Thus answer is C.
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by saurabhmahajan » Tue Sep 21, 2010 2:24 am
X mts / Sec = Y Km/ Hr

converting km to mts and hrs to sec
so, X/S=Y*1000/3600

therefore now Y= 3600X / 1000 S
solving this we will get Y= 18X/5
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by GMATGuruNY » Tue Sep 21, 2010 3:21 am
Gurpinder wrote:Image
Since the answer choices contain a variable, we can plug in.

Let x = 10 meters/sec.
1 hour = 3600 seconds, so every hour we'll go r*t = 10*3600 = 36000 meters = 36 kilometers.
Thus, y = 36 kilometers/hour. This is our target answer.

Now we plug x=10 into all the answer choices to see which yields our target answer of 36.

Only answer choice C works:
18x/5 = 18*10/5 = 36.

The correct answer is C.
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