what is y in terms of x? (GMAT Prep)

[alex.gellatly]

If the speed of x meters per second is equivalent to the speed of y kilometers per hour, what is y in terms of x? (1kilometer = 1,000 meters)

5x/18
6x/5
18x/5
60x
3600000x

[Anurag@Gurome]

If the speed of x meters per second is equivalent to the speed of y kilometers per hour, what is y in terms of x?

x meters = x/1000 kilometers
1 second = 1/3600 hours

Hence, x meters per second = (x/1000 kilometers)/(1/3600 hours) = 3600x/1000 kilometers per hour

Therefore, y = 3600x/1000 = 36x/10 = 18x/5

The correct answer is C.

[GMATGuruNY]

If the speed of x meters per second is equivalent to the speed of y kilometers per hour, what is y in terms of x? (1kilometer = 1,000 meters)

5x/18
6x/5
18x/5
60x
3600000x

Let x = 1 meter per second.
Since there are 3600 seconds in an hour, the distance traveled in one hour = 3600 meters = 3.6 kilometers.
Thus, y = 3.6 = 36/10 = 18/5. This is our target.

Now we plug x=1 into the answer choices to see which yields our target of 18/5.
A quick scan reveals that only C works:
18x/5 = (18*1)/5 = 18/5.

The correct answer is C.