<PRE><B>Question 524457</B>
Dave takes a group of teenagers on a canoe trip on the Wolf River.
 He discovers that it takes him the same amount of time to paddle 4 miles upstream as it does to paddle 16 miles downstream.
 If Dave can paddle 5 miles per hour in still water, how fast is the current?
:
Let c = rate of the current
then
(5-c) = effective speed upstream
and
(5+c) = effective speed down stream
:
Write a time equation; time = dist/speed
:
Time up = time down
{{{4/((5-c))}}} = {{{16/((5+c))}}}
Cross multiply
4(5+c) = 16(5-c)
20 + 4c = 80 - 16c
4x + 16c = 80 - 20
20c = 60
c = 60/20
c = 3 mph is the rate of the current
:
:
Check this by finding the actual time of each
4/(5-3) = 2 hrs
16/(5+3)= 2 hrs</PRE>