<PRE><B>Question 532666</B>
The speed of a stream is 5 mph. If a boat travels 72 miles downstream in the same time that it takes to travel 36 miles upstream, what is the speed of the boat in still water?
----
Downstream DATA:
distance = 72 miles ; rate = b+5 mph ; time = 72/(b+5) hrs.
----
Upstream DATA:
distance = 36 miles ; rate = b-5 mph ; time = 36/(b-5) hrs
----
Equation:
time = time
72(b+5) = 36/(b-5)
-------
2/(b+5) = 1/(b-5)
Cross-multiply to get:
2b-10 = b+5
b = 15 mph (speed of the boat in still water)
===================
Cheers,
Stan H.
===================</PRE>