SOLUTION: It takes a crew 1 hour and 30 minutes longer to go 12 miles upstream than to return. Find their rate in still water if the rate of the current is 2mph.

Question 392018: It takes a crew 1 hour and 30 minutes longer to go 12 miles upstream than to return. Find their rate in still water if the rate of the current is 2mph.
Answer by mananth(16946) (Show Source): You can put this solution on YOUR website!
It takes a crew 1 hour and 30 minutes longer to go 12 miles upstream than to return. Find their rate in still water if the rate of the current is 2mph.
..
let speed of boat be x mph
current speed = 2 mph.
upstream speed = x-2 mph
downstream speed = x-2 mph
..
time = distance / speed
upstream time -downstream time = 1 1/2 = 3/2 hours

LCD = (x+2)(x-2)
multiply by (x+2)(x-2)
..
x(x+2)-x(x-2)/(x+2)(x-2) = 3/2
x^2+2x-x^2+2x/(x+2)(x-2)=3/2
4x/(x+2)(x-2)= 3/2
cross multiply
8x= 3(x+2)(x-2)
8x=3x^2-12
3x^2-8x-12=0
Find roots by quadratic equation
b^2-4ac=208

x1= 3.73 mph speed of boat.
x2 is negative so ignore
...
m.ananth@hotmail.ca
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