Mr Tortoise completes the race at an average speed of 20 km/hr. His average speed for the first two stretches is four times that for the last stretch. Find the speed over stretch C.
Explanation:
Let his average speed over the last stretch be x.
Hence, his average speed for first two stretches = 4x. So the total time taken to cover the three stretches =44x+2x
His average speed over the race is 20 km/hr.
Hence, the time taken to complete the race = 620
Hence, we have the equation 44x+2x=620 Solving this equation, we get x = 10 km/hr.
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