SOLUTION: A BOAT TRAVELS 8KM UPSTREAM AND 8KM BACK. TIME FOR THE ROUND TRIP IS 9HRS. THE SPEED OF THE STREAM IS 5KM/HR. WHAT IS THE SPEED OF THE BOAT IN STILL WATER?

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Question 321379: A BOAT TRAVELS 8KM UPSTREAM AND 8KM BACK. TIME FOR THE ROUND TRIP IS 9HRS. THE SPEED OF THE STREAM IS 5KM/HR. WHAT IS THE SPEED OF THE BOAT IN STILL WATER?

Answer by galactus(183) About Me  (Show Source):
You can put this solution on YOUR website!
Let r be the rate of the stream.
Then, upstream the boat travels at a rate of 5-r
Downstream, it travels at a rate of 5+r
Since d=rt, then t=d/r.
The trip takes 9 hours altogether, so we have:
8%2F%285%2Br%29%2B8%2F%285-r%29=9
Solving for r gives us r=sqrt%28145%29%2F3=4.01 km/hr