<PRE><B>Question 500351</B>
Mike drove uphill to his school and it took 3 hours.
 He returned downhill only going 5 mph faster and made it in two hours.
 What is the average rate of speed?
:
Find the one-way distance first
let d = the one-way distance
:
Write a speed equation; speed = dist/time
:
up speed + 5 mph = down speed
{{{d/3}}} + 5 = {{{d/2}}}
multiply by 6, to clear the denominators
2d + 6(5) = 3d
30 = 3d - 2d
d = 30 mi one way
:
Find the average speed for the round trip (60 mi)
Total time for the round trip: 2 + 3 = 5 hrs
:
write a speed equation, speed = dist/time
:
{{{60/5}}} = 12 mph is the average speed for the round trip</PRE>