SOLUTION: I really need help on this problem. 84. Gone fishing. Debbie traveled by boat 5 miles upstream to fish in her favorite spot. Because of the 4-mph current, it took her 20 minut

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Question 338781: I really need help on this problem.
84. Gone fishing. Debbie traveled by boat 5 miles upstream to
fish in her favorite spot. Because of the 4-mph current, it
took her 20 minutes longer to get there than to return. How
fast will her boat go in still water?
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
Debbie traveled by boat 5 miles upstream
4-mph current,
took her 20 minutes longer to get there
to return.
speed of boat in still water = x mph
speed upstream = x-4
speed down stream = x=4
..
time upstream = 5/(x-4)
time downstream = 5/(x+4)
time upstream - time donstream = 1/3 hour ( 20 minutes)
5%2F%28x-4%29-5%2F%28x%2B4%29=+1%2F3
LCD = (x+4)(x-4)
%285%28x%2B4%29-5%28x-4%29%29%2F%28x%5E2-16%29=+1%2F3
%285x%2B20-5x%2B20%29%2F%28x%5E2-16%29=1%2F3
40%2F%28x%5E2-16%29=1%2F3
3*40=x^2-16
120 = x^2-16
x= 11.66 mph speed of boat in still water
..
CHECK
plug the value of x in the equation
(5/(11.66-4))-(5/(11.66+4))= 0.333
x^2=136