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

Question 69719: "Rita rows 12 km upstream and 12 km downstream in three hours. The speed of her boat in still water is 9 km/hr. Find the speed of the stream."
Thanks.
Found 2 solutions by checkley75, josmiceli:
Answer by checkley75(3666) (Show Source): You can put this solution on YOUR website!
12/(9+x)+12/(9-x)=3
[12(9-x)+12(9+x)]/(9+x)(9-x)=3
(108-12x+108+12x)/(81-x^2)=3
216/(81-x^2)=3
3(81-x^2)=216
243-3x^2-216=0
-3x^2+27=0
x^2=-27/-3
x^2=9
x=3 which is the current
proof
12/(9-3)+12(9+3)=3
12/6+12/12=3
2+1=3
3=3

Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!

s = speed of stream

multiply both sides by (9+s)(9-s)

km/hr answer
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