Question 933065
Let 3km = the distance the boat traveled
    5kph= the speed of the stream

a boat travels 3km upstream and 3km back. the time for the round trip is 10 hours. the speed of the stream is 5 km/hr.
Distance = (rate)(time)
time     =  Distance/rate
rate     =  Distance/time


3/(x+5) + 3/(x-5)=10
(3x-15 + 3x+15)/(x+5)(x-5)= 10
6x/(x+5)(x-5)=10
          6x =10(x+5)(x-5)
          6x =10 (x^2-25)
          3x =5 (x^2-25)
          3x =5x^2-125
           0 =5x^2-3x-125

{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}
{{{x = (-(-3) +- sqrt( (-3)^2-4*(5)*(-125) ))/(2*(5)) }}}
{{{x = (3 +- sqrt( 9+2500 ))/(10) }}}
{{{x = (3 +- sqrt( 2509 ))/(10) }}}

x= 5.30899191454728 or 5
or
x= -4.70899191454728 or -5

The boat's speed is 5kph.