Copyright © University of Cambridge. All rights reserved.
'Tyre Wear' printed from https://nrich.maths.org/
Answer: 24000 km
Of the $5$ tyres, $4$ are used at any one time, so each tyre is used for $\frac{4}{5}$ of the journey, or $$\frac{4}{5} \times 30000 \; \text{km} = 24000 \; \text{km}$$