Marco rode his dirt bike at 45 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? Choose the correct choice
A) 14 mph  B) 20 mph  C) 70/3 mph  D) 80/3 mph  E) 34 mph
Average speed for first two hours, S1 = 45 mph   Distance travelled in these two hours, D1 = 90 miles   Average speed for the entire 5 hour ride, S = 30 mph   Total Distance traveller in the entire 5 hour ride, D = 30 x 5 = 150 miles.   Hence, distance traveller in the latter 3 hour period, D2 = D - D1 = 150 - 90= 
<gadget id="calculator">150 - 90</gadget>
<output>60</output>
60   Average speed for the latter 3 hour period S2= D2/3 = 60/3= 
<gadget id="calculator">60/3</gadget>
<output>20</output>
20   Hence, the correct answer is 20 mph
<result>B</result>
Marco rode his dirt bike at 45 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?