A boat travels upstream, against a current, at a speed of 4 miles per hour. On the return trip, the boat travels downstream,with the current, at 10 miles per hour. The speed of the current remains constant. What is the speed of the current?

Solution:

        Let speed of current = umph

            speed of boat in still water = v mph

            v + u = 10

            v - u = 4

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Adding 2v = 14

               v = 14/2 = 7

              u = 10 - 7 = 3 mph