Julie and eric row their boat (at a constant speed) 63 miles downstream for 7 hours by the current. rowing at the same rate, the trip back against the current takes 9 hours. find the rate of the boat in still water.

Boat speed = 8 miles/hr

Explanation:

Let the speed of the boat be U

Let the speed of the current be V.

Therefore, the downstream speed is U+V

and the upstream speed is U-V

Now we know that Speed = distance / time

Therefore, downstream speed, U+V = 63 / 7

                                                    U+V = 9 miles/hr   (1)

                  Upstream speed, U-V = 63 / 9

                                                U-V = 7 miles/hr      (2)

Therefore subtracting (2) from (1), we get

( U+V) - ( U-V ) = 9-7

2V = 2

V = 1 miles/hr

Therefore the speed of the current is V = 1 mile/hr

Now from (1) we get

U+V = 9

U+1 = 9

U = 8

Therefore, the speed of the boat is U = 8 miles/hr

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