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Question
Solve the following linear programming problem graphically:
Minimize z = 6 x + 3 y
Subject to the constraints:
4 x + \[y \geq\] 80
x + 5 \[y \geq\] 115
3 x + 2 \[y \leq\] 150
\[x \geq\] 0 , \[y \geq\] 0
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Solution
The given constraints are
4x + y \[\geq\] 80
x + 5y \[\geq\] 115
3x + 2y \[\geq\] 150
x,y \[\geq\] 0
Converting the given inequations into equations, we get
4x + y = 80, x + 5y = 115, 3x + 2y = 150, x = 0 and y = 0
These lines are drawn on the graph and the shaded region ABC represents the feasible region of the given LPP.
It can be observed that the feasible region is bounded. The coordinates of the corner points of the feasible region are A(2, 72), B(15, 20) and C(40, 15).
The values of the objective function, Z at these corner points are given in the following table:
| Corner Point | Value of the Objective Function Z = 6x + 3y |
| A(2, 72) | Z = 6 × 2 + 3 × 72 = 228 |
| B(15, 20) | Z = 6 × 15 + 3 × 20 = 150 |
| C(40, 15) | Z = 6 × 40 + 3 × 15 = 285 |
From the table, Z is minimum at x = 15 and y = 20 and the minimum value of Z is 150.
Thus, the minimum value of Z is 150.
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