SOLUTION: Please help! I really need to learn how to do travel word problems and they confuse me so much. The speed of a river's current is 4 miles per hour. You travel 2 miles with the

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Question 571707: Please help! I really need to learn how to do travel word problems and they confuse me so much.
The speed of a river's current is 4 miles per hour. You travel 2 miles with the current and then return to where you started in a total time of 1.25 hours. What is your speed in the still water in miles per hour?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
The speed of a river's current is 4 miles per hour.
You travel 2 miles with the current and then return to where you started in a total time of 1.25 hours.
What is your speed in the still water in miles per hour?
:
let s = the speed of your boat in still water
then
(s-4) = your effective speed up-stream
and
(s+4) = your effective speed down-stream
:
Write a time equation; time = dist/speed
:
Time upstr + time downstr = 1.25 hrs
2%2F%28%28s-4%29%29 + 2%2F%28%28s%2B4%29%29 = 1.25
Multiply by (s-4)(s+4)
(s+4)*s-4)2%2F%28%28s-4%29%29 + (s+4)(s-4*2%2F%28%28s%2B4%29%29 = 1.25(s+4)(s-4)
Cancel the denominators, and you have
2(s+4) + 2(s-4) = 1.25(s^2-16)
:
2s + 8 + 2s - 8 = 1.25s^2 - 20
Combine to form a quadratic equation
0 = 1.25s^2 - 4s - 20
You have to use the quadratic equation to find s
only on solution will make sense, I got
5.91 mph is his approx speed in still water