Question
Shankar covers a certain distance by a car driving at 40
km/h and he returns to the starting point riding on a scooter with a speed of 20 km/h. Find the average speed of the whole journey.Solution
Let the distance one way be d km. Time taken by car = d / 40 Time taken by scooter = d / 20 Total Distance = d + d = 2d Total Time = (d / 40) + (d / 20) Total Time = d(1/40 + 1/20) Total Time = d(1/40 + 2/40) Total Time = d(3/40) Total Time = 3d / 40 Average Speed = (2d) / (3d / 40) ⇒ Average Speed = (2d × 40) / 3d ⇒ Average Speed = 80d / 3d ⇒ Average Speed = 80 / 3 ⇒ Average Speed = 26 (2/3) km/h The average speed for the whole journey is 26 (2/3) km/h.
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