SOLUTION: A boat can go 72 miles downstream in 3 hours, and can make the return trip in 4 hours. Find the speed of the boat in still water.

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Question 858150: A boat can go 72 miles downstream in 3 hours, and can make the return trip in 4 hours. Find the speed of the boat in still water.
Answer by tommyt3rd(5050) About Me  (Show Source):
You can put this solution on YOUR website!
up: (s+c)3=72,
down: (s-c)4=72
adding...
2s=72(1/3+1/4)
then...
s=21
boat speed: 21mph