A motorcyclist drives A to B with a uniform speed of 30 kmph and returns back with a speed of 20 kmph. Find its average speed.

If any object travel from one point to another point speed ${\text{v}}_{\text{1}}$ and return to same point with another speed ${\text{v}}_{\text{2}}$ , its average speed can be calculated by

${\text{v}}_{\text{avg}}=\frac{2{\text{v}}_{\text{1}}{\text{v}}_{\text{2}}}{{\text{v}}_{\text{1}}+{\text{v}}_{\text{2}}}$

$\left({\text{v}}_{\text{1}}=30\text{kmph},{\text{v}}_{\text{2}}=20\text{kmph}\right)$

$=\frac{2\times 30\times 20}{30+20}$

$=\frac{2\times 30\times 20}{50}$

$=2\times 6\times 2=24\text{kmph}$