If the speed of X meters per second is equivalent to the

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BTGmoderatorDC: Moderator; Posts: 7187; Joined: Thu Sep 07, 2017 4:43 pmFollowed by: 23 members

by BTGmoderatorDC » Mon Aug 06, 2018 11:55 pm

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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? (1 kilometer=1000 meters)

A. 5x/18
B. 6x/5
C. 18x/5
D. 60x
E. 3600000x

OA C

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GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members; Location: New York, NY; Thanked: 13060 times; GMAT Score:790

by GMATGuruNY » Tue Aug 07, 2018 3:46 am

BTGmoderatorDC wrote: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? (1 kilometer=1000 meters)

A. 5x/18
B. 6x/5
C. 18x/5
D. 60x
E. 3600000x

Plug in for x a value that is easy to convert from meters to kilometers.

Let x = 1000 meters per second.
Since 1000 meters = 1 kilometer, this rate = 1 kilometer per second.
Since there are 3600 seconds in an hour, 1 kilometer per second = 3600 kilometers per hour.
Thus, y = 3600. This is our target.

Now plug x = 1000 into the answer choices to see which yields our target of 3600.
Only C works:
18x/5 = (18*1000)/5 = 3600.

The correct answer is C.

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Tue Aug 07, 2018 5:43 am

BTGmoderatorDC wrote: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? (1 kilometer=1000 meters)

A. 5x/18
B. 6x/5
C. 18x/5
D. 60x
E. 3600000x

We want to convert meters per second to kilometers per hour

First, since 1 kilometer = 1000 meters, we can also say that 1 kilometer/1000 meters = 1
Second, since 3600 seconds = 1 hour, we can also say that 3600 seconds/1 hour = 1

This means that multiplying a value by 1 kilometer/1000 meters is the SAME AS multiplying that same value by 1.
Likewise, multiplying a value by 3600 seconds/1 hour is the SAME AS multiplying that same value by 1.

So, x meters/second = x (meters/second)(1)(1)
= x (meters/second)(1 kilometer/1000 meters)(3600 seconds/1 hour)
= x (3600/1000)(kilometers/hour) [after all of the "unwanted" units cancel out]
= x (18/5)(kilometers/hour)
= 18x/5 kilometers/hour
= C

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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Jeff@TargetTestPrep: GMAT Instructor; Posts: 1462; Joined: Thu Apr 09, 2015 9:34 amFollowed by: 22 members; Location: New York, NY; Thanked: 39 times

by Jeff@TargetTestPrep » Sat Aug 18, 2018 6:54 pm

BTGmoderatorDC wrote: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? (1 kilometer=1000 meters)

A. 5x/18
B. 6x/5
C. 18x/5
D. 60x
E. 3600000x

There are 3,600 seconds in an hour and 1,000 meters in a kilometer. So, let's convert y kilometers/hour to meters/second:

We can start by converting y kilometers to meters.

y kilometers = 1,000y meters

Next we can convert 1 hour to seconds.

1 hour = 3,600 seconds

Thus, y km/hr can be expressed as 1,000y/3,600 m/sec, or 5y/18 m/sec, after it's simplified.

Since our two rates are equal, x = 5y/18. We need to solve this equation for y.

18x = 5y

18x/5 = y

Answer: C

Jeffrey Miller
Head of GMAT Instruction
[email protected]

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