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

Question 114533: Rita rows 12km upstream and 12km downstream in 3 hours. The of her boat in still water is 9km/hr. Find the speed of the stream.
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
Rita rows 12km upstream and 12km downstream in 3 hours. The of her boat in still water is 9km/hr. Find the speed of the stream.
:
Totally unrealistic, no one can row a boat at 9 km/hr, however......
:
Let x = speed of the stream
:
(9+x) = speed downstream
and
(9-x) = speed upstream
:
Write a time equation: Time = distance/speed
:
Time up + time down = 3hrs
+ = 3
:
Get rid of the denominators, multiply equation by (9+x)(9-x) and you have:
12(9+x) + 12(9-x) = 3(9+x)(9-x)
:
108 + 12x + 108 - 12x = 3(81 - x^2)
:
216 = 243 - 3x^2
:
+3x^2 = 243 - 216
:
3x^2 = 27
:
x^2 =
:
x^2 = 9
:
x = 3 km/hr is the current
:
:
Check solution:
12/12 + 12/6 = 3 hrs
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