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A body cover 20 kilometre with a speed of 40 km/hand next 20 km with a speed of 30 km per hour calculate average speed |
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Answer» A body cover 20 kilometre with a speed of 40 km/h time taken, t₁ = 20/40 = 1/2 h It covered NEXT 20 km with a speed of 30 km/h time taken, t₂ = 20/30 = 2/3 h total time taken = t₁ + t₂ = 1/2 + 2/3 = (3+4)/6 = 7/6 h total distance traveled = 20+20 = 40km AVERAGE speed = total distance/total time ⇒ average speed = 40/(7/6) = 40×6/7 ⇒ average speed = 240/7 km/h = 34.28 km/h --------------------------------------------------------------------------- Another shortcut: You see that it travels 20km each time with different speed. When distance travelled each time is same and it travels at speed x and y, average speed can be calculated as: average speed = 2XY/(x+y) using this, average speed = 2×30×40/(30+40) = 34.28 km/h |
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