SOLUTION: Patty the Paddler paddles her paddle boat at a constant 12km/h. She paddles 21km upstream and 34 km downstream in a total of 5 hours. What is the speed of the current?

Question 211498: Patty the Paddler paddles her paddle boat at a constant 12km/h. She paddles 21km upstream and 34 km downstream in a total of 5 hours. What is the speed of the current?
Answer by checkley77(12844) (Show Source): You can put this solution on YOUR website!
D=RT
T=D/R
X=21/(12-R)
12X-RX=21
5-X=34/(12+R)
X=21/(12-R)
--------------
5=34/(12+R)+21/(12-R)
5=[34(12-R)+21(12+R)]/(12+R)(12-R)
5=[408-34R+252+21R]/(144-R^2)
5(144-R^2)=13R+660
720-5R^2-13R-660=0
-5R^2-13R+60=0
5R^2-13R-60=0
(5R+12)(R-5)=0
R-5=0
R=5 KM/H. ANS. FOR THE CURRENT.
PROOF:
5=34/(12+5)+21/(12-5)
5=34/17+21/7
5=2+3

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