SOLUTION: 1- In a river that flows at 3 mph, a boat takes 1 hour longer to sail 36 miles upstream than to return. Find the speed of the boat in still water.

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Question 205995: 1- In a river that flows at 3 mph, a boat takes 1 hour longer to sail 36 miles upstream than to return. Find the speed of the boat in still water.
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
In a river that flows at 3 mph, a boat takes 1 hour longer to sail 36 miles
upstream than to return.
Find the speed of the boat in still water.
:
Let s = speed of boat in still water
then
(s+3) = speed downstream
and
(s-3) = speed upstream
:
Write a time equation
:
time downstream = time upstream - 1 hr
36%2F%28%28s%2B3%29%29 = 36%2F%28%28s-3%29%29 - 1
:
Multiply equation by (s+3)(s-3), results
36(s-3) = 36(s+3) - (s+3)(s-3)(1)
:
36s - 108 = 36s + 108 - (s^2 - 9)
:
36s - 108 = 36s + 108 - s^2 + 9
:
Combine like terms on the left:
s^2 + 36s - 36s - 108 - 108 - 9 = 0
:
s^2 - 225 = 0
:
s^2 = 225
s = sqrt%28225%29
s = 15 mph, speed in still water
:
:
Check solution by finding the times
36/(15-3) = 3 hrs
36/(15+3) = 2 hrs
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differs by: 1 hr