SOLUTION: It takes a boat 4 hours to travel 56 miles down a river, and 3 hours longer to make the return trip. Find the speed of the current.

What is asked in the problem?

Find the speed of the current?



Given:

It takes a boat 4 hours to travel 56 miles down the river

3 hours longer to make a return trip.



Representation:

Let x = speed of the boat in still water 

    y = speed of the current



Make a table for the information given:

                 r         t      =      d

Downstream      x+y        4      =      56

Upstream        x-y       4+3     =      56



Write an Equation:

4 (x + y) = 56

7 (x - y) = 56



       x + y = 14

       x - y = 8

       __________



          2x = 22

           x = 11 miles/hour   <<<<< speed of the boat in still water



 x + y = 14

11 + y = 14

     y = 3 miles/hour <<<<<<<<< speed of the current



Checking:    

4 (x + y) = 56 , x = 11, y = 3

4(11 + 3) = 56

    4(14) = 56

       56 = 56 ----------->> True







7 (x - y) = 56, x = 11, y = 3

7(11 - 3) = 56

    7 (8) = 56

       56 = 56  ------->> True