Excluding stoppages, the average speed of a bus is 60 km/hr and including stoppages, the average speed of the bus is 20 km/hr. For how many minutes does the bus stop per hour? Choose the correct choice from the following answers:
A) 22  B) 88  C) 77  D) 40  E) 99
In 1hr, the bus covers 60 km without stoppages and 20 km with stoppages.   Stoppage time = time take to travel (60 - 20) km i.e 40 km at 60 km/hr.   stoppage time = 40/60 hrs = 40 min.   Answer: 40
<result>D</result>
Excluding stoppages, the average speed of a bus is 60 km/hr and including stoppages, the average speed of the bus is 20 km/hr. For how many minutes does the bus stop per hour?