Return speed for a target average

EasyBrainteasers~3m

You drive to work at 40 mph. You want your round-trip average speed (same route both ways) to be 60 mph. How fast (in mph) must you drive on the return leg?

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Average speed is total distance over total time, not the mean of the two speeds.
Set $\frac{2}{1/40 + 1/v} = 60$ and solve for $v$ .

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Return speed for a target average

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