MathRevolution wrote:

[GMAT math practice question]

If Alice traveled on a 10 km trip at a constant speed of 25 km/h and a 48 km trip at a constant speed of 30 km/h, what was her average speed, in kilometers per hour, for the two trips?

A. 26 km/h

B. 28 km/h

C. 29 km/h

D. 30 km/h

E. 32 km/h

Average speed = \(\frac{TotalDistance}{TotalTime}\)

Trip 1, time, \(T=\frac{D}{r}\)

\(T=\frac{10mi}{25mph}=\frac{2}{5}\) hour

Trip 2, time, \(T=\frac{48mi}{30mph}=\frac{8}{5}\)hour

Total distance: (10 + 48) = 58 miles

Total time: \((\frac{2}{5}+\frac{8}{5})hrs=\frac{10}{5}hrs=2hrs\)

Ave. speed = \(\frac{TotalD}{TotalT}=\frac{58mi}{2hr}=29\) mph

Answer C