Excluding stoppages, the average speed of a bus is 50 km/hr and including stoppages, the average speed of the bus is 40 km/hr. For how many minutes does the bus stop per hour? Choose the most appropriate option:
A) 12 min  B) 18 min  C) 16 min  D) 20 min  E) 26 min

Rationale: "in 1 hr , the bus covers 50 km without stoppages and 40 km with stoppages . stoppage time = time take to travel ( 50 - 40 ) km i . e 10 km at 50 km / hr . stoppage time = 10 / 50 hrs = 12 min answer : a"
Answer: A