<PRE><B>Question 742105</B>
The speed of a boat in still water is 8 km/h.
 It travels 60 km upstream and 60 km downstream in a total time of 16 hours.
 What is the speed of the stream?
:
Let c = rate of the current
then
(8+c) = effective speed downstream
and
(8-c) = effective speed upstream
:
Write a time equation; time = dist/speed
:
Time upstr + time down = 16 hrs
{{{60/((8+c))}}} + {{{60/((8-c))}}} = 16
multiply equation by (8-c)(8+c) canceling the denominators, you have
60(8-c) + 60(8+c) = 16(8-c)(8+c)
:
480 - 60c + 480 + 60c = 16(64-c^2)
:
960 = 1024 - 16c^2
:
16c^2 = 1024 - 960
16c^2 = 64
c^2 = 64/16
c^2 = 4
c = {{{sqrt(4)}}}
c = 2 mph is the rate of the current
:
:
See if that checks out, find the actual time each way
60/6 = 10 hrs
60/10= 6 hrs
---------------
total 16 hrs
</PRE>