Question 830714
A man goes at the speed of 5 km/hour from P to Q and returns at the speed of 3 km/hour from Q to P.
 The average speed of whole journey is:
:
Let a = average speed for the whole journey
Let d = the distance one way
:
Write a time equation, time = dist/speed
{{{d/5}}} + {{{d/3}}} = {{{(2d)/a}}}
multiply equation by 15a, cancel the denominators and you have:
3ad + 5ad = 15(2d)
8ad = 30d
divide both sides by d
8a = 30
a = 30/8
a = 3.75 mph