<PRE><B>Question 338451</B>
in still water, a boat averages 7 mph.
 it takes the same amount of time to travel 20 miles downstream, with the 
current, as 8 miles upstream, against the current. 
what is the rate of the water&#39;s current?
:
Let c = rate of the current
then
(7+c) = effective rate downstream
and
(7-c) = effective rate upstream
:
Write a time equation: time = dist/rate
:
Time downstr = time upstr
{{{20/(7+c)}}} = {{{8/(7-c)}}}
Cross multiply
20(7-c) = 8(7+c)
140 - 20c = 56 + 8c
140 - 56 = 8c + 20c
84 = 28c
c = {{{84/28}}}
c = 3 mph is the current rate
;
:
:
Check this by finding the times
20/10 = 2 hrs
8/4 = 2 hrs</PRE>