SOLUTION: a river boat tour begins by going 60 miles upstream against a 5 mph current. Then the boat turns around and returns with the current. What still-water speed should the captain us

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Question 416168: a river boat tour begins by going 60 miles upstream against a 5 mph current. Then the boat turns around and returns with the current. What still-water speed should the captain use to complete the tour in 5 hours?
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
let speed in still water =x mph
current speed 4 mph

upstream speed = x-4
downstream speed = x+4

Distance= 60 miles

Time upstream + time downstream = 5 hours
t=d/r
60/(x+4)+60(x-4)=5
LCD =(x -4)(x+4)
60*(x-4)+60(x+4)=5
60x-240 +60x+240=5(X^2-16)
120x=5X^2-80
5X^2-120x-80
a= 5, b= -120, c=-80
b^2-4ac= 12800
x1=%28120%2Bsqrt%2812800%29%29%2F%2810%29
x1=23.3 mph
x2=%28120-sqrt%2812800%29%29%2F%2810%29
=0.69 -- not practical