A man walks 30 km at 5 km/h and runs 40 km at 10 km/h. Find average speed.

A. 6.5 km/h
B. 6.8 km/h
C. 7 km/h
D. 7.5 km/h

Solution:
Time = 30/5 + 40/10 = 6+4=10 h
Total distance = 70
Average speed = 70/10= 7 km/h
Answer: C