Excluding stoppages, the average speed of a bus is 60 km/hr and including stoppages, the average speed of the bus is 30 km/hr. For how many minutes does the bus stop per hour?  Choose the correct option:
A) 22
B) 30
C) 77
D) 20
E) 99

Rationale: "in 1 hr , the bus covers 60 km without stoppages and 30 km with stoppages . stoppage time = time take to travel ( 60 - 30 ) km i . e 30 km at 60 km / hr . stoppage time = 30 / 60 hrs = 30 min . answer : b"
Answer: B