SOLUTION: A river flows at a rate of 4 km./hr. for the length of its scenic route. In order for a boat to travel the 60 km. upriver and then return in a total of 8 hours, how fast must the b

Question 327892: A river flows at a rate of 4 km./hr. for the length of its scenic route. In order for a boat to travel the 60 km. upriver and then return in a total of 8 hours, how fast must the boat be able to travel in still water?
Answer by mananth(16946) (Show Source): You can put this solution on YOUR website!
60/(x-4)+60/(x+4)= 8
60(x+4)+60(x-4)/ (x^2-16)=8
60x+240+60x-240=8(x^2-16)
120x=8x^2-128
add -120x to both sides
120x-120x = 8x^2-120x-128
8x^2-120x-128=0
divide by 8
x^2-15x-16=0
x^2-16x+x-16=0
x(x-16)+1(x-16)=0
(x-16)(x+1)=0
x= 16 OR -1 ignore negative value
So the speed in still water = 16
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