Question
A driver covers a distance in three stages. In the first
'z - 50' km, he drives at 40 km/h, for the next 'z' km at 60 km/h, and the remaining 'z + 50' km at 50 km/h. If the overall average speed is 50 km/h, calculate 'z'.Solution
ATQ, Let the total distance covered is: (z−50)+z+(z+50)=3z The total time taken is the sum of the time for each segment: 
Then, Average Speed Equation: Average Speed= (Total Distance/Total Time) = 50 km/h 
Now, Set Up the Equation: 
Then, solve for 'z' Find a common denominator (600) and combine terms: 
Cross-multiply and solve: 1800z = 1850z - 7500 7500 − 50z = -7500 z = 150
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