A person travels a distance of 300 m and then returns to the starting point. The time taken by him for the outward journey is 5 hours more than the time taken for the return journey. If he returns at a speed of 10 km/h more than the speed of going, what is the average speed (in km/h) for the entire journey?

$$\eqalign{ & \frac{{300}}{{x + 10}} - \frac{{300}}{x} = 5 \cr & 60\left[ {\frac{{10}}{{x\left( {x + 10} \right)}}} \right] = 1 \cr & 600 = x\left( {x + 10} \right) \cr & {\text{Put }}x = 20 \cr & {\text{Average speed}} = \frac{{2 \times 20 \times 30}}{{20 + 30}} \cr & = \frac{{2 \times 600}}{{50}} \cr & = 24{\text{ km/hr}} \cr} $$