22. Lewis drives from London to Brighton at an average speed of $60 \mathrm{mph}$. On the way back, he gets stuck in traffic and his average speed is only $40 \mathrm{mph}$. What is his average speed for the whole journey?
A $55 \mathrm{mph}$ B $50 \mathrm{mph}$ C $48 \mathrm{mph}$ D $45 \mathrm{mph}$ E Impossible to determine
22. C Let the distance from London to Brighton be $d$ miles. Since time $=$ distance $/$ speed, the times Lewis spent on the two parts of his journey are $\frac{d}{60}$ hours and $\frac{d}{40}$ hours. Hence the total time in hours that he travelled is
$$
\frac{d}{60}+\frac{d}{40}=\frac{2 d+3 d}{120}=\frac{5 d}{120}=\frac{d}{24} .
$$

Therefore his average speed for the whole journey is $2 d \div\left(\frac{d}{24}\right) \mathrm{mph}=48 \mathrm{mph}$.