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[email protected]: Master | Next Rank: 500 Posts; Posts: 429; Joined: Wed Sep 19, 2012 11:38 pmFollowed by: 4 members; Thanked: 6 times

by [email protected] » Fri Sep 20, 2013 6:34 pm

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. 15x/18
B. 6x/5
C. 18x/5
D. 60x
E. 3600000x

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Source: Beat The GMAT — Problem Solving | Fri Sep 20, 2013 6:34 pm

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 » Fri Sep 20, 2013 6:56 pm

[email protected] 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. 15x/18
B. 6x/5
C. 18x/5
D. 60x
E. 3600000x

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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theCodeToGMAT: Legendary Member; Posts: 1556; Joined: Tue Aug 14, 2012 11:18 pmFollowed by: 34 members; Thanked: 448 times; GMAT Score:650

by theCodeToGMAT » Fri Sep 20, 2013 7:57 pm

X m/s = Y km/h

Even though X & y are equivalent; they are not yet equal because of different units

For example:
1 Minute = 60 Seconds ..... (this is equivalency)
BUT, that doesnt mean 1==60 ( you need to balance the units)

So,

X ( 3600/1000) km/h = Y km/h
18X/5 = Y

ANSWER [spoiler][C][/spoiler]

R A H U L

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vinay1983: Legendary Member; Posts: 643; Joined: Wed Aug 14, 2013 4:27 amFollowed by: 7 members; Thanked: 48 times

by vinay1983 » Fri Sep 20, 2013 8:41 pm

I had used a similar formula for certain exams

If you want to convert speed given in km/hr, then to get the same in m/s multiply the original speed in km/hr by 5/18

Then to convert from m/s to km/hr multiply m/s by 18/5

Hope it helps!

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by Brent@GMATPrepNow » Sat Sep 21, 2013 6:13 am

[email protected] 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. 15x/18
B. 6x/5
C. 18x/5
D. 60x
E. 3600000x

Although I prefer Mitch's method, here's the algebraic approach.

To convert meters/second to km/hour, we must recognize that 1 meter = (1/1000)km and 1 second = (1/3600)hour

So, 1 meter/second = 1 (1/1000)km / (1/3600)hour
= 1 (3600/1000) km/hour
= 1 (36/10) km/hour
= (18/5) km/hour

So, if 1 meter/second = (18/5) km/hour, then x meters/second = [spoiler]x(18/5) km/hour[/spoiler]
= C

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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by [email protected] » Sat Sep 21, 2013 10:06 am

Hi shibsriz,

Each of the above explanations is valid/fast way to approach this question. Mitch's explanation (to TEST values), is my preferred approach, so I thought I'd offer an alternative way to tackle this question using THAT tactic.

Normally, in these situations, you shouldn't use the numbers 0 or 1. However, since the answers are significantly different from one another and the variable (x) does not appear in the denominator of the answers, I'm going to use x = 1

So, 1 meter/sec = 60 meters/min = 3600 meters/hr

3600 m/hr = 3.6 km/hr

Plug x = 1 in to the answers and find 3.6

Only answer C matches.

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Last edited by [email protected] on Sun Sep 22, 2013 12:03 pm, edited 1 time in total.

Contact Rich at [email protected]

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faraz_jeddah: Master | Next Rank: 500 Posts; Posts: 358; Joined: Thu Apr 18, 2013 9:46 amFollowed by: 7 members; Location: Jeddah, Saudi Arabia; Thanked: 42 times; GMAT Score:730

by faraz_jeddah » Sun Sep 22, 2013 12:54 am

vinay1983 wrote:I had used a similar formula for certain exams

If you want to convert speed given in km/hr, then to get the same in m/s multiply the original speed in km/hr by 5/18

Then to convert from m/s to km/hr multiply m/s by 18/5

Hope it helps!

Yup! Used this in high school physics. God bless the Indian education system

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