New objective value -
Old objective value
= =
2212.5 - 2200 12.5
An extra hour of finishing time increases the contribution by £12.5. The normal cost of finishing time is already included in the objective which measures contribution not revenue. The dual value (£12.5) should be compared with the extra overtime cost of finishing time (£8). Since it is greater, overtime should be used. Marking scheme Out of 20: Marks Formulation Graphical solution Knowing how to find dual values Calculation of new optimal solution Calculation of new optimal objective Calculation of dual values Interpretation of dual values
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20
Let x = number of bags of JDJ. Let y = number of bags of PRP.
There are constraints for the requirements of each of nitrogen, phosphorus and potassium. If x bags of JDJ are used, then 40x kg of JDJ are used (40 kg per bag). Since JDJ contains 20% nitrogen compounds, the quantity of nitrogen applied will be 20% of 40x, i.e. 8x kg.