A person walks 10km at a speed of 2.5 km/hr, then runs 10 km at a speed of 5 km/hr and then goes 30 km by bus at the speed of 30 km/hr. What is the average speed of the man?

7.14 km/hr 

Average speed = $\frac {total\; distance}{total\; time}$

Time = $\frac{distance}{speed}$

When the speed is 2.5 km/hr

Time = $\frac{10}{2.5}$ = 4 hours 

When the speed is 5 km/hr,

Time = $\frac{10}{5}$ = 2 hours 

When the speed is 30 km/hr,

Time = $\frac{30}{30}$ = 1 hour 

Total time = 7 hours

Thus, average speed = $\frac{50}{7}$ = 7.14 km/hr