<PRE><B>Question 338781</B>
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/(x-4)-5/(x+4)= 1/3}}}
LCD = (x+4)(x-4)
{{{(5(x+4)-5(x-4))/(x^2-16)= 1/3}}}
{{{(5x+20-5x+20)/(x^2-16)=1/3}}}
{{{40/(x^2-16)=1/3}}}
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</PRE>