Travelling to some place and back again might involve travelling twice the distance of only travelling there, but might well not mean taking twice as long. Going in one direction might mean travelling uphill or going against the wind or travelling in rush hour, meaning that this part of the total journey takes longer.
To find a total time or the speed over one or both parts of the journey can involve setting up an equation to be solved.
The distance from London to Brighton is 55 miles. The average speed from Brighton to London is
mph and the average speed from London to Brighton is
mph. The total travel time is 2 hours. Find
The Brighton to London journey takes
hours
The London to Brighton journey takes
hours.
The total journey takes 2 hours so
We have to solve the equation
We can start by multiplying by
to clear all the fractions, giving
or
mph. The second of these is obviously wrong so
mph.