Problem Solving

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

OA D.

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.

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.

Regards!