SOLUTION: A boat travels 30 miles upstream in 4 hours. The trip downstream takes 2.5 hours. Find the rate of the boat in still water.

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Question 74470: A boat travels 30 miles upstream in 4 hours. The trip downstream takes 2.5 hours. Find the rate of the boat in still water.
Answer by scott8148(6628) About Me  (Show Source):
You can put this solution on YOUR website!
Going upstream: rate-current=30 mi/4 hr or 7.5 mph
Going downstream: rate+current=30 mi/2.5 hr or 12 mph

Adding upstream and downstream:

rate-current + rate+current=7.5 mph + 12 mph ; +/- currents cancel

2*rate=19.5 mph ; rate=9.75 mph