SOLUTION: A boat travels 3 km upstream and 3 km back. The time for the round trip is 7 hrs. The speed of the stream is 4 ​km/hr. What is the speed of the boat in still​ water?

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Question 1140221: A boat travels 3 km upstream and 3 km back. The time for the round trip is 7 hrs. The speed of the stream is 4 ​km/hr. What is the speed of the boat in still​ water?
Answer by josgarithmetic(39625)   (Show Source): You can put this solution on YOUR website!
               SPEED       TIME         DISTANCE

upstream         r-4       3/(r-4)        3

downstream       r+4       3/(r+4)        3

TOTAL                       7

-----simplify and solve.
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