SOLUTION: The world's strongest current, reaching 10 miles per hour, is the Saltstraumen in Norway. A motor boat can travel 60 miles downstream in the Saltstraumen in the same time it takes

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: The world's strongest current, reaching 10 miles per hour, is the Saltstraumen in Norway. A motor boat can travel 60 miles downstream in the Saltstraumen in the same time it takes       Log On


   

Question 1075931: The world's strongest current, reaching 10 miles per hour, is the Saltstraumen in Norway. A motor boat can travel 60 miles downstream in the Saltstraumen in the same time it takes to go 20 miles up stream. What is the speed of the boat in still water?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
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The world's strongest current, reaching 10 miles per hour, is the Saltstraumen in Norway.
A motor boat can travel 60 miles downstream in the Saltstraumen in the same time it takes to go 20 miles up stream.
What is the speed of the boat in still water?
f:
let s = speed of the boat in still water
then
(s-10) = effective speed upstream
and
(s+10) = effective speed downstream
:
Write a time equation; time = dist/speed
60%2F%28%28s%2B10%29%29 = 20%2F%28%28s-10%29%29
cross multiply
60(s-10) = 20(s+10)
distribute
60s - 600 = 20s + 200
Combine s on the left, numbers on the right
60s - 20s = 200 + 600
40s = 800
s = 800/40
s = 20 mph in still water
:
;
Confirm this find the actual time each way, find the effective speed
60/30 = 2 hrs
20/10 = 2 hrs