<PRE><B>Question 949015</B>
a boat can travel 48 mph in still water.
 If it travels 486 miles with the current in the same length of time it travels 378 miles against the current, what is the speed of the current?
:
let c = rate of the current (in mph)
then
(48-c) = the effective speed upstream
and
(48+c) = effective speed downstream
:
Write a time equation; time = dist/speed
 {{{378/((48-c))}}} = {{{486/((48+c))}}}
Cross multiply
378(48+c) = 486(48-c)
18144 + 378c = 23328 - 486c
378c + 486c = 23328 - 18144
864c = 5184
c = 5184/864
c = 6 mph is the the current
:
;
Check this, find the actual times, should be equal
Speed with the current = 54 and speed against = 42
486/54 = 9 hrs
378/42 = 9 hrs</PRE>