Question
A motor-cycle covers 125 km with a speed of 60 km/hr.
find the speed of the motor-cycle for the next 125 km journey so that the average speed of the whole journey will be 80 km/hr.Solution
Average speed of whole journey = 80 km/hr Using the formula, average speed = 2xy/(x + y) ⇒ x = speed of first 125 km = 60 km/hr ⇒ 80 = 2 × (60 × y)/(60 + y) ⇒ 120 km/hrÂ
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