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If Judy rows at the rate of 7 mph against the current, and 11mph with the current, what is the average speed of her trip if she goes the same distance in both directions?

 Feb 22, 2021
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total distance / total time = average        time = distance/rate

 

d = distance

 

d / 7  + d/11=   2d /average

 

1/7 + 1/11 = 2/average

average = 2 / (1/7 + 1/11) = 154/18 = 77/9 m/hr =   8.56  m/hr

 Feb 22, 2021

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