swerve wrote:The latest model of space shuttle can achieve a maximum speed of 25 miles per second. This maximum speed is how many miles per hour?

A. 1,500
B. 3,600
C. 9,000
D. 15,000
E. 90,000
Source: Princeton Review

\[25\,\,{\text{miles}}\,\,{\text{per}}\,\,{\text{second}}\,\,\,\, = \,\,\,?\,\,\,{\text{mph}}\]
Let´s use UNITS CONTROL, one of the most powerful tools of our method!
\[?\,\, = \,\,\,\frac{{25\,\,{\text{miles}}}}{{1\,\,{\text{second}}}}\,\,\,\left( {\frac{{60\,\,{\text{seconds}}}}{{1\,\,{\text{minute}}}}} \right)\,\,\,\,\left( {\frac{{60\,\,{\text{minutes}}}}{{1\,\,{\text{h}}}}} \right)\,\,\,\,\mathop = \limits^{\left( * \right)} \,\,\,\,90,000\,\,\]
\[\left( * \right)\,\,\,25 \cdot 60 \cdot 60\,\, = \,\,\,25 \cdot 4 \cdot 15 \cdot 4 \cdot 15 = 100 \cdot 225 \cdot 4 = 100 \cdot 900\]

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

Regards,
Fabio.