speed/conversion problem

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speed/conversion problem [#permalink]

04 Jun 2009, 21:39

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Hey guys, was wondering if anyone could offer a way to solve this problem:

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

answer: C.

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Re: speed/conversion problem [#permalink]

05 Jun 2009, 02:47

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To convert Y Km/Hr to Metre/second just multiply it by 1000/(60*60)

1000Y/3600 and this is equal to X

Hence 1000Y/3600 = X => Y = 18X/5

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Re: help solving problem [#permalink]

09 May 2010, 22:40

y=18/5x

meters-->km is a factor of 1000

seconds --> hrs is a factor of 3600 (or 60sec/min times 60min/hr)

3600/1000 = 18/5. Did I do this right?

Let me try slower:

Meters/sec times 1KM/1000meter =KM/sec; Km/sec times 60 sec/min times 60 min/hr =km/hr. so we divide by 1000 and multiply by 3600. Yep I think I got it.

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Re: help solving problem [#permalink]

10 May 2010, 02:25

Is it not 5/18 and not 18/5 ?

km/hr is Y
m/s is X

what is Y in terms of X implies express Y in X which is

1000/3600X = 10/36X

Y=5/18X.

Please correct.

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Re: speed/conversion problem [#permalink]

14 Dec 2010, 00:48

For conversions try to understand the basic fundamental through the below explanation;

Example #1)

1 mile= 1.61km

so 15.7 miles =? km

Soln:
PRINCIPLE/METHODOLOGY:

Convert the eqn to a fraction with the desired units on top and the given units on the bottom i.e. to convert from miles to kilometers you need a fraction with the desired units (KM in our case) on THE TOP and the given units (Miles) on THE BOTTOM.

= 1.61km/1mile

Now the solution becomes 15.7miles * 1.61 Km /1 mile = 25.3km (Note how the miles in the num & deno cancel and we are left with km - as what the question asked.Keep this principle in mind)

Example #2)

7miles/sec is how many miles / hour?

Soln: 1 hr= 3600 sec
In the question given units (sec) are in the denominator of the original measurement, so seconds must be in the numerator of the conversion function.

1 hr= 3600 sec
i.e 1=3600/1hr

7miles/sec x 3600 sec/hr =7x 3600 = 25000 miles /hr . (Note the seconds get cancelled)

Example#3)

12 cubic yards = how many cubic feet?

Given: 1 yard= 3 feet .
i.e 1 =3feet/1 yard

Therefore 12 yd^3 * (3ft/1yd)^3
= 12 * 3^3 * yd^3 x ft^3 / yd^3 = 12 x 27 ft^3 (Note that the yd^3 gets cancelled out in Num & Deno)

= 324 ft^3 (Ans)

COMING BACK TO YOUR ORIGINAL QUESTION , solution as follows,
x mtr/sec= y km/hour

Therefore in terms of x calculate as follows,

xmtr/sec * 60sec/1min * 60min/1hr * 1km/1000mtr

= 18x/5 (note how the mtr,sec & min cancell out in the numerator and denominator giving us what we required)

Answer C

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Re: speed/conversion problem [#permalink]

14 Dec 2010, 02:10

scorpio7 wrote:

X meters per second -->
--> 3,600X meters per hour (as there are 3,600 seconds in one hour);
--> 3,600X/1,000=18X/5 kilometers per hour (as there are 1,000 meters in one kilometer).

Answer: C.

Or if you are not comfortable with above manipulations with variable X then you can assume x to be equal to some #: let x=10.

Speed = 10 meters per second -->
--> 10*3,600=36,000 meters per hour -->
--> 36,000/1000=36 kilometers per hour.

So, if x=10, then y=36. Plug x=10 into the answer choices, the one which give 36 will be the correct answer:
A. 15x/18=150/18<36;
B. 6x/5=60/5=12;
C. 18x/5=36 correct choice;
D. 60x=600;
E. 3,600,000x=36,000,000.

Answer: C.
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Re: speed/conversion problem [#permalink]

14 Dec 2010, 20:59

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scorpio7 wrote:

Unit conversion is a quick process:
\frac{X meters}{1 second} = \frac{Y km}{1 hour}

Replace a km by 1000 m and 1 hour by 3600 seconds
\frac{X meters}{1 second} = \frac{Y * 1000 meters}{3600 seconds}

Units get canceled and we are left with:
\frac{18X}{5} = Y

Check out my blog post for more examples:
http://gmatquant.blogspot.com/2010/11/converting-units-its-one-step-process.html
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Re: speed/conversion problem [#permalink]

14 Dec 2010, 21:42

(X)(m/s) = (Y)(Km/hr) = (Y)(1000m/60*60s)
Y=(X)*((60*60)/1000) = 3.6X = 18X/5

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Re: help solving problem [#permalink]

25 Dec 2010, 08:01

I think it's \frac{18x}{5}

Can someone please double check?

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Re: help solving problem [#permalink]

25 Dec 2010, 08:15

Y=X* 60*60/1000
=>Y= X*36/10
=> Y=X*18/5
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HELP for a Gmat prep question [#permalink]

06 Jan 2011, 08:55

Hello guys,

I can't figure out this problem :

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

5x/18

6x/5

18x/5

60x

3 600 000x

THANKS !!

HELP for a Gmat prep question [#permalink] 06 Jan 2011, 08:55

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