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.
:
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