SOLUTION: It took a crew 6 h 24 min to row 6 km upstream and back again. If the rate of flow of the stream was 7 km/h, what was the rowing speed of the crew in still water?

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Question 646016: It took a crew 6 h 24 min to row 6 km upstream and back again. If the rate of flow of the stream was 7 km/h, what was the rowing speed of the crew in still water?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
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It took a crew 6 h 24 min to row 6 km upstream and back again.
If the rate of flow of the stream was 7 km/h, what was the rowing speed
of the crew in still water?
:
Change 6 hrs, 24 min to hrs, 6 + 24/60 = 6.4 hrs
:
Let s = rowing speed in still water
then
(s-7) = effective speed upstream
and
(s+7) = effective speed downstream
:
Write time equation, time = dist/speed
:
6%2F%28%28s-7%29%29 + 6%2F%28%28s%2B7%29%29 = 6.4
multiply by (s-7)(s+7), obtain a quadratic equation and solve