Question 634512
A bicyclist rode from point A to Point B at an average speed of 30 km/hr.
 Without stopping, he returned from Point B to Point A, following the same
 route, at an average speed of 20 km/hr.
 What was the average speed in km/hr over the course of the ride?
:
Let a = the average speed for the round trip
Let d = one-way distance
:
Write a time equation, time = dist/speed
:
A-B time + B-A time = Total time
{{{d/30}}} + {{{d/20}}} = {{{(2d)/a}}}
We don't need d, divide thru by d
{{{1/30}}} + {{{1/20}}} = {{{(2)/a}}}
multiply by 60a, resulting in
2a + 3a = 2(60)
5a = 120
a = 120/5
a = 24 km/h is the average speed for the round trip