<PRE><B>Question 67179</B>
It took 3 hours to row a boat 18 km against the current, The return trip with the current took 1 1/2 hours. Find the speed of the rowboat in still water.
:
Let s = boat speed in still water
Let c = current speed:
:
Speed with the current: (s+c)
Speed against the current: (s-c)
:
Dist = time * speed:
:
3(s - c) = 18
Simplify divide both sides by 3
s - c = 6
:
1.5(s + c) = 18
Simplify divide both sides by 1.5
s + c = 12
:
Add these equations and eliminate c
s - c = 6
s + c = 12
-----------  add
2s + 0 = 18
2s = 18
s = 9 mph is the speed in still water
:
:
Find the current to check our solution:
9 + c = 12
c = 3 mph
:
3(9-3) = 18
1.5(9+3) = 18
1.5(s+c) = 18</PRE>