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Determining a constant speed based on previous and average speed

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A motorist makes a trip of 180 miles. For the first 90 miles, she drives at a constant speed of
30 mph. At what constant speed must she drive the remaining distance, if her average speed for
the total trip is to be 40 mph?

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Solution Preview

The average speed for the whole trip is simply given by:

Va = DISTANCE TRAVELED/TIME TAKEN = D/T

Va = average speed, D = distance traveled (total), T = total time traveled.

It is easy to think that

Va = (v1+v2)/2, but this is incorrect, use the formula above. From the problem we can ...

Solution Summary

This solution explains how to determine a constant speed based on previous and average speeds.

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