A car travels the first half of a total distance with a speed of 20text{ m/s} and the second half with a speed of 30text{ m/s}. The average speed of…

Let total distance be $2d$. Time taken for the first half is $t_1 = \frac{d}{20}$ and for the second half is $t_2 = \frac{d}{30}$. Average speed = $\frac{\text{Total distance}}{\text{Total time}} = \frac{2d}{\frac{d}{20} + \frac{d}{30}} = \frac{2}{\frac{3+2}{60}} = \frac{120}{5} = 24\text{ m/s}$.