Question
A traveler moves a distance in three intervals. In the
first 'u - 15' km, he travels at 20 km/h, in the next 'u' km at 40 km/h, and completes the journey of 'u + 15' km at 30 km/h. If the average speed for the entire trip is 30 km/h, what is 'u'?Solution
ATQ, The traveler covers three distances: u−15 km at 20 km/h u km at 40 km/h u+15 km at 30 km/h The average speed for the entire trip is 30 km/h. 
Given the average speed is 30 km/h: 
Solve for u: Simplify the equation to get: 
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