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The aerth travels around the sun at a speed of approximately

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The earth travels around the sun at a speed of approximately

by fskilnik@GMATH » Tue Sep 11, 2018 9:58 am
AAPL wrote:GMAT Prep

The earth travels around the sun at a speed of approximately 18.5 miles per second. The approximate is how many miles per hour?

A. 1,080
B. 1,160
C. 64,800
D. 66,600
E. 3,996,000
Trivial application of the UNITS CONTROL, one of our method´s most powerful techniques!
\[?\,\,\, = \,\,\,\frac{{18.5\,\,{\text{miles}}}}{{1\,\,{\text{s}}}}\,\,\,\left( {\frac{{60\,\,{\text{s}}}}{{1\,\,{\text{minute}}}}\,\,\begin{array}{*{20}{c}}
\nearrow \\
\nearrow
\end{array}} \right)\,\,\,\,\left( {\frac{{60\,\,{\text{minutes}}}}{{1\,\,{\text{h}}}}\,\,\begin{array}{*{20}{c}}
\nearrow \\
\nearrow
\end{array}} \right)\,\,\,\, = \,\,\frac{{37}}{2} \cdot 36 \cdot 100 = 37 \cdot 18 \cdot 100 = 66,600\,\,\,\left[ {{\text{mph}}} \right]\]
Obs.: arrows indicate licit converters.

This solution follows the notations and rationale taught in the GMATH method.

Regards,
fskilnik.
Fabio Skilnik :: GMATH method creator ( Math for the GMAT)
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by swerve » Tue Sep 11, 2018 10:05 am
This is a classic case of approximations as the options are too widespread.

18.5 mps to 18.5 mph with 1 h = 3600 seconds.

Thus 18.5 mps = 18.5*3600 = a bit more than 18*3600 = a bit more than 18*18*200 = a bit more than 324*2*100 = a bit more than 64800 . So eliminate C and mark D is the correct answer.

You need to remember squares from 1 to 20 for GMAT.

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by Brent@GMATPrepNow » Tue Sep 11, 2018 10:16 am
Another way to deal with calculating (18.5)(3600) is to use the answer choices to our advantage.

First off, there's a nice rule that says: AB = (2A)(0.5B)
This strategy (which is covered in this video: https://www.gmatprepnow.com/module/gene ... video/1113) can sometimes save us some calculations.

When we apply the rule, (18.5)(3600) = (37)(1800) [I doubled 18.5 to get 37, and I halved 3600 to get 1800 ]
= (37)(18)(100)
= (----6)(100) [We know that the units digit of 37 x 18 must be 6, since 7 x 8 = 56]
= ---600 [some number that ends with 600]

Check the answer choices....
A. 1,080
B. 1,160
C. 64,800
D. 66,600 BINGO!!
E. 3,996,000

Cheers,
Brent
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by Scott@TargetTestPrep » Wed Sep 12, 2018 5:28 pm
AAPL wrote:GMAT Prep

The earth travels around the sun at a speed of approximately 18.5 miles per second. The approximate is how many miles per hour?

A. 1,080
B. 1,160
C. 64,800
D. 66,600
E. 3,996,000
Since 1 second = 1/3600 hours, the rate in miles per hour is:

18.5/(1/3600) = 18.5 x 3600 = 66,600

Answer: D

Scott Woodbury-Stewart
Founder and CEO
[email protected]

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