SOLUTION: the current in a stream moves at a speed of 9 mph. A boat travels 22 mi upstream and 22 mi downstream in a total time of 5 hrs. what is the speed of the boat in still water

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Question 961328: the current in a stream moves at a speed of 9 mph. A boat travels 22 mi upstream and 22 mi downstream in a total time of 5 hrs. what is the speed of the boat in still water
Answer by lwsshak3(11628) About Me  (Show Source):
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the current in a stream moves at a speed of 9 mph. A boat travels 22 mi upstream and 22 mi downstream in a total time of 5 hrs. what is the speed of the boat in still water
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let x=speed of boat in still water
x+9=speed of boat downstream
x-9=speed of boat upstream
..
travel time=distance/speed
22%2F%28x%2B9%29%2B22%2F%28x-9%29=5
lcd: (x+9)(x-9)
22/(x-9)+22/(x+9)=5(x+9)(x-9)
22x+198+22x-198=5(x^2-81)
44x=5x^2-405
5x^2-44x-405=0
solve for x by quadratic formula:
x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+
a=5, b=-44, c=-405
ans: x=14.4
what is the speed of the boat in still water? 14.4 mph