SOLUTION: I am having a difficult time with this problem. 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 str
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Question 69986: I am having a difficult time with this problem. 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. Someone please help?
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
I am having a difficulty time with this problem. 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.
:
let x = speed of the stream:
:
Speed upstream = (9-x)
Speed downstream = (9+x)
:
Time = dist/speed
:
Time upstream + time downstream = 3 hrs
:
= 3
:
Multiply equation by (9-x)(9+x), results
:
12(9+x) + 12(9-x) = 3(9-x)(9+x)
:
108 + 12x + 108 - 12x = 3(81 - x^2); difference of squares
:
216 = 243 - 3x^2; 12x's eliminated
:
0 = 243 - 216 - 3x^2
:
+3x^2 = 243 - 216
:
3x^2 = 27
:
x^2 = 27/3
:
x^2 = 9
:
x = SqRt(9)
:
x = 3 mph speed of the stream
:
:
Check our solution: speed up is 6, speed down is 12
12/12 + 12/6 = 3 hrs
:
Did this make sense to you?
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