posted by marie .
A motor boat took 4 hours to make a downstream trip with a current of 3mph. The return trip against the same current took 8 hours. Find the speed of the boat in still water.
Call Y the boat's rate.
distance = rate x time.
downstream rate of boat is Y+3. t=4 hrs.
upstream rate of boat is Y - 3. t=8 hrs.
d(downstream) = (Y+3)4
d(upstream) = (Y-3)8
The distance is the same so set them equal to each other and solve for Y.