A bus driver must complete a 240 km trip in 4 hours. If he averages 70 km an hour for the first 3 hours of his trip, how fast must he travel (in km/h) in the last/final hour?

Total distance to be covered = 240 km Total time available = 4 hours Distance covered in the first 3 hours: ⇒ Distance = Speed × Time ⇒ Distance = 70 km/h × 3 hours ⇒ Distance = 210 km Remaining distance to be covered in the final hour: ⇒ Remaining distance = Total distance - Distance covered in the first 3 hours ⇒ Remaining distance = 240 km - 210 km ⇒ Remaining distance = 30 km Speed required to cover the remaining distance in the final hour: ⇒ Speed = Distance / Time ⇒ Speed = 30 km / 1 hour ⇒ Speed = 30 km/h ∴ The bus driver must travel at 30 km/h in the last hour.