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?
Answer & explanation
Correct answer: option 3
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