Question 154845
A cyclist bikes x distance at 10 miles per hour and returns over the same path at 8 miles per hour. Whast is the cyclist's average rate for the round trip in miles per hour?
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1st leg DATA:
distance = x miles ; rate = 10 mph ; time = d/r = x/10 hrs
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Return leg DATA:
distance = x miles ; rate = 8 mph ; time = d/r = x/8 hrs
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Average rate = (total distance)/(total time)
= 2x/[(x/10) + x/8] 

= 2x/[18x/80]

= 2x/[9x/40]

= 80/9

= 8.89 mph
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Cheers,
Stan H.