BTGmoderatorDC wrote: ↑

Mon Apr 13, 2020 4:46 pm

Marco rode his dirt bike at 40 miles per hour (mph) for two hours. If he then continued to ride at a different constant rate for another three hours, and at the end of the three hours his average speed for the entire five hour ride was 30mph, what was his average speed over the three hour portion of his ride?

A. 14 mph
B. 20 mph
C. 70/3 mph
D. 80/3 mph
E. 34 mph


OA C

Source: Veritas Prep

Average speed for the first two hours, \(S_1 = 40\) mph
Distance traveled in these two hours, \(D_1 = 80\) miles

Average speed for the entire 5 hour ride, \(S = 30\) mph
Total Distance traveller in the entire 5 hour ride, \(D = 30 \cdot 5 = 150\) miles.

Hence, distance traveller in the latter 3 hour period, \(D_2 = D - D_1 = 150 - 80 = 70\)
Average speed for the latter 3 hour period \(S_2 = \dfrac{D_2}{3} = \dfrac{70}{3}\)

Hence, the correct answer is C