SOLUTION: Rita rows 12 km upstream and 12 km downstream in 3 hours. The speed of her boat in still water is 9 km/hr. Find the speed of the stream

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Question 114437: Rita rows 12 km upstream and 12 km downstream in 3 hours. The speed of her boat in still water is 9 km/hr. Find the speed of the stream
Answer by stanbon(75887) (Show Source):
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Rita rows 12 km upstream and 12 km downstream in 3 hours. The speed of her boat in still water is 9 km/hr. Find the speed of the stream
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Let speed of the stream be "s"
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Upstream DATA;
distance = 12 km ; Rate = 9-s km/h; Time = d/r = 12/(9-s) hrs.
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Downstream DATA:
distance = 12 km ; Rate = 9+s; Time = 12/(9+s) hrs.
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EQUATION:
time up + time down = 3 hrs
12/(9-s) + 12/(9+s) = 3
1/(9-s) + 1/(9+s) = 1/4
4(9+s) + 4(9-s) = 9^2-s^2
72 = 81-s^2
x^2 = 9
s = 3
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Cheers,
Stan H.