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Question 13 Marks
Solve the Linear Programming Problem graphically:
Minimize Z = -3x + 4y subject to $x + 2y \leq 8, \ 3x + 2y \leq 12, \ x \geq 0, \ y \geq 0.$
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Question 23 Marks
Show that the minimum of Z occurs at more than two points.
Maximize Z = x + y, subject to $x - y \leq - 1, - x + y \leq 0, \ x, \ y \geq 0$.
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Question 33 Marks
Solve the Linear Programming Problem graphically:
Maximise Z = 3x + 4y subject to the constraints: $x + y \le4, \ x \geq 0, \ y \geq 0$
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Question 43 Marks
Solve the following linear programming problem graphically:
Minimise Z = 200x + 500y subject to the constraints:
$x + 2 y \geq 10$
$3 x + 4 y \leq 24$
$x \geq 0 , y \geq 0$
Answer
According to the question, the linear constraints
$x + 2 y \geq 10$
$3 x + 4 y \leq 24$
and $x \geq 0 , y \geq 0$
and objective function is Min $(Z) = 200x + 500y.$
Reducing the above inequations into equations
$x + 2y = 10$ ...(i)
$3x + 4y = 24$ ...(ii)
$x = 0, y = 0$ ...(iii)

Equations Point of Intersection
(i) and (ii) x = 4 and y = 3
$\Rightarrow$ Point is $ (4, 3)$
(i) and (iii) when x = 0 $\Rightarrow$ y = 5
when y = 0 $\Rightarrow$ x = 10
$\Rightarrow$ Points are $(0, 5), (10, 0)$
(ii) and (iii) when x = 0 $\Rightarrow$ y = 6
when y = 0 $\Rightarrow$ x = 8
$\Rightarrow$ Points are $(0, 6) and (8, 0)$


For $x + 2 y \geq 10$, putting x = 0 and y = 0
$\Rightarrow 0 + 0 \geq 10 \Rightarrow 0 \geq 10$ i.e., Not true
$\Rightarrow$ The shaded region will be away from origin.
Likewise, for $3 x + 4 y \leq 24$, putting x = 0 and y = 0 $\Rightarrow 0 + 0 \leq 24 \Rightarrow 0 \leq 24$ i.e. true
$\Rightarrow$ the shaded region will be toward the origin
Also, we have, $x \geq 0$ and $y \geq 0$, indicates that the shaded part will exist in first quadrant only. Here, feasible region or bounded region will be $ABCA$, having corner points as $A(0,6) B(4, 3)\ and\ C(0, 5)$. For optimal point substituting the value of all-corner points in $Z = 200x + 500y$

Corner points Z
$A (0, 6)$ $3000$
$B (4, 3)$ $2300$ $\to$ Minimum
$C (0, 5)$ $2500$

$\Rightarrow$ The minimum value of ‘Z’ is 2300, exist at B (4, 3). Here point B is known as optimal point and min(Z) as optimal solution.

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Question 53 Marks
Solve the following linear programming problem graphically:
Maximise Z = 4x + y subject to the constraints:
x + y $\le$ 50
3x + y $\le$ 90
x $\ge$ 0, y $\ge$ 0
Answer
To Maximize Z = 4x + y ......(i)
subject to the constraints:
x + y $\le$ 50 .....(ii)
3x + y $\le$ 90 ......(iii)
x $\ge$ 0, y $\ge$ 0 .....(iv)
The shaded region in a figure is the feasible region determined by the system of constraints (ii) to (iv). We observe that the feasible region OABC is bounded. So, we now use Corner Point Method to determine the maximum value of Z.
The coordinates of the corner points O, A, B and C are (0, 0), (30, 0), (20, 30) and (0, 50) respectively. Now we evaluate Z at each corner point.

Corner Point Corresponding value of Z
(0, 0) 0
(30, 0) 120
(20, 30) 110
(0, 50) 50


Hence, maximum value of Z is 120 at the point (30, 0).

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3 Marks Question - Maths STD 12 Science Questions - Vidyadip