Given: Abdul goes from city A to city B at the speed of 40 km/hr and returns a speed of 60 km/hr. Total time taken by him is 10 hours. Formula Used: Average Speed = Total distance/Total time taken Total time taken = Total distance/Average Speed Calculation: Let the distance covered from A to B be x km. Time taken from city A to city B = x/40 = x/40 hours Time taken from city B to city A = x/60 = x/60 hours Total time = 10 hours ⇒ x/40 + x/60 = 10 ⇒ x × 10/240 = 10 ⇒ x = 240 km The distance travelled = 240 km ∴ The distance between A and B is 240 km. [ height="46px" src="//storage.googleapis.com/tb-img/production/22/02/60756f21213996ac19669dae_16442451297951.png" width="240px"> Average speed = 2 × S1 × S2/(S1 + S2) Average speed = 2 × 40 × 60 /(60 + 40) = 48 km/hr The distance between A and B = (48 × 10)/2 = 480/2 = 240 km ∴ The distance between A and B is 240 km.