SOLUTION: A man rows a boat 630 feet upstream against a constant current in 18 minutes. He then rows 405 feet downstream (with the same current) in 9 minutes. Find the speed of the current a

Question 924656: A man rows a boat 630 feet upstream against a constant current in 18 minutes. He then rows 405 feet downstream (with the same current) in 9 minutes. Find the speed of the current and the equivalent rate at which he can row in still water.
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
A man rows a boat 630 feet upstream against a constant current in 18 minutes.
He then rows 405 feet downstream (with the same current) in 9 minutes.
Find the speed of the current and the equivalent rate at which he can row in still water.
:
let s = his rowing speed in still water in ft/min
let c = the speed of the current
then
(s-c) = effective speed upstream
and
(s+c) = effective speed downstream
write a distance equation for each way.(dist = time*speed)
18(s-c) = 630
9(s+c) = 405
simplify both equations, divide the 1st by 18 and the 2nd by 9
we can use elimination very easily here
s - c = 35
s + c = 45
-------------Adding eliminates c, find s
2s = 80
s = 40 ft/min in still water
:
:
Check this, find the speed of the current
40 + c = 45
c = 5 ft/min
then the effective speed upstream will be 35 ft/min
18 * 35 = 630 ft

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