SOLUTION: Speed: A boat travels 36 miles down a river in 3 hours. If it takes the boat 9 hours to travel the same distance going up the river, what is the speed of the boat? What is the sp

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Question 54953: Speed: A boat travels 36 miles down a river in 3 hours. If it takes the boat 9 hours to travel the same distance going up the river, what is the speed of the boat? What is the speed of the current of the river?
Answer by rapaljer(4671) About Me  (Show Source):
You can put this solution on YOUR website!
Let x = speed of the boat in still water
y = speed of the current of the river

x+y = rate downstream
x-y = rate upstream

Distance = Rate * Time, so
Rate+=+Distance%2FTime

x+y=36%2F3=12 Downstream
x-y=36%2F9=4 Upstream

Add these two equations together:
2x = 16, so x = 8 mph in still water

x+y = 12, where x = 8, y = 4 mph current.

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