Planning with limiting factors
               3.1   Step 1: define the variables
                  Example 2, continued
                   Let 'x' be the number of units of X to produce
                   Let 'y' be the number of units of Y to produce
               3.2   Step 2: the objective function
                  Example 2, continued
                   Objective function: to maximise contribution C = 4x + 8y
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