Given: Average speed = 20 km/hr Rides for 20 minutes at a speed of 15 km/hr Rides for 30 minutes at a speed of 10 km/hr Concept Used: Speed = Distance/Time Average speed = Total distance travelled/Total time taken Calculation: According to the first condition, ⇒ 15 km/hr = Distance/ 20 minutes ⇒ 15 = Distance/ (20/60) hours ⇒ 15 = Distance/(1/3) ⇒ Distance = 5 km According to the second condition, ⇒ 10 km/hr = Distance/30 minutes ⇒ 10 = Distance/(30/60) hours ⇒ 10 = Distance/(1/2) hours ⇒ Distance = 5 km Now in the last phase he drives his scooter for 10 minutes. ⇒ Total time = 20 minutes + 30 minutes + 10 minutes ⇒ Total time = 60 minutes ⇒ Total time = 1 hour Let the distance covered by him in the last phase be x ⇒ Total distance covered = 5 + 5 + x ⇒ Total distance covered = 10 + x Average speed = Total Distance covered/Total time taken ⇒ 20 = (10 + x)/ 1 hour ⇒ 20 = 10 + x ⇒ x = 20 – 10 ⇒ x = 10 ⇒ The distance covered by him in the last phase is 10 km. ⇒ Speed in the last phase = 10 km/10 minutes ⇒ Speed in the last phase = 10 km/(10/60)hours ⇒ Speed in the last phase = 10 × 6 ⇒ Speed in the last phase = 60 km/hr ∴ His speed in the last phase is 60 km/hr.