Question 1158426
Let's say that the boat can travel x km/hr on still water. It can travel (x-5) km/hr upstream and (x+5) km/hr downstream. {{{2/(x-5)+2/(x+5)=4}}}. {{{2(x+5)/(x-5)(x+5)+2(x-5)/(x-5)(x+5)=4(x+5)(x-5)/(x+5)(x-5)}}} {{{2(x+5)+2(x-5)=4(x-5)(x+5)}}}. {{{2x+10+2x-10=4x^2-100}}}. {{{4x^2-4x-100=0}}} {{{x^2-x-25=0}}} *[invoke complete_square "x",1,-1,-25] <br/> The boat can travel about 5.525 km/hr.