Excluding stoppages, the average speed of a bus is 120 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?
Select the correct option.
A) 15 min  B) 18 min  C) 16 min  D) 20 min  E) 40 min

Rationale: "in 1 hr , the bus covers 120 km without stoppages and 40 km with stoppages . stoppage time = time take to travel ( 120 - 40 ) km i . e 80 km at 120 km / hr . stoppage time = 80 / 120 hrs = 40 min answer : e"
Answer: E