Question
A bike covers 60 km with a speed of 20 km/hr. Find the
speed of the bike for the next 50 km journey so that the average speed of the whole journey will be 30 km/hr.Solution
Let the speed for the next 50 km be x kmph. Average Speed = Total Distance/Total Time Total Distance = 60 + 50 = 110 km Total Time = 60/20 + 50/x = (3 + 50/x) hours => 30 = 110/(3 + 50/x) => 90 + 1500/x = 110 => 110x – 90x = 1500 => 20x = 1500 => x = 75 kmph
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