Excluding stoppages, the speed of a bus is 50 kmph and including stoppages, it is 35 kmph.For how many minutes does the bus stop per hour? Pick one
A) 17 minutes  B) 18 minutes  C) 19 minutes  D) 16 minutes  E) none of these

Rationale: "explanation : in one hour due to stoppages , it covers 15 km less . time taken to cover 15 km = [ 15 / 50 * 60 ] min = 18 min answer : b"
Answer: B