Class CBSE Class 12 Mathematics Linear Programming Q #1387
COMPETENCY BASED
UNDERSTAND
3 Marks 2025 AISSCE(Board Exam) SA
Solve the following linear programming problem graphically: Minimise $Z=x-5y$ subject to the constraints: $x-y\ge0$, $-x+2y\ge2$, $x\ge3$, $y\le4$, $y\ge0$.

AI Tutor Explanation

Powered by Gemini

Detailed Solution

Step 1: Graph the Constraints

First, we graph the constraints on the $x$-$y$ plane. The constraints are: $x - y \ge 0$ $-x + 2y \ge 2$ $x \ge 3$ $y \le 4$ $y \ge 0$

Step 2: Identify the Feasible Region

The feasible region is the intersection of all the constraint regions. We need to find the vertices of this feasible region.

Step 3: Find the Intersection Points

We find the intersection points of the lines that form the boundaries of the feasible region. \r\n1. Intersection of $x = y$ and $-x + 2y = 2$: \r\nSubstituting $x = y$ into the second equation, we get $-y + 2y = 2$, so $y = 2$. Thus, $x = 2$. However, $x \ge 3$, so this intersection is not in the feasible region. \r\n2. Intersection of $x = 3$ and $x = y$: \r\nSince $x = 3$, $y = 3$. So the point is $(3, 3)$. \r\n3. Intersection of $x = 3$ and $y = 4$: \r\nThis point is $(3, 4)$. \r\n4. Intersection of $y = 4$ and $-x + 2y = 2$: \r\nSubstituting $y = 4$ into the second equation, we get $-x + 2(4) = 2$, so $-x + 8 = 2$, which means $x = 6$. So the point is $(6, 4)$. \r\n5. Intersection of $y = 0$ and $x=y$: \r\nThis point is $(0,0)$. However, $x \ge 3$ and $-x+2y \ge 2$, so this point is not in the feasible region. \r\n6. Intersection of $y = 0$ and $-x+2y=2$: \r\nSubstituting $y=0$ into the second equation, we get $-x+2(0)=2$, so $x=-2$. However, $x \ge 3$, so this point is not in the feasible region. \r\n7. Intersection of $x=3$ and $-x+2y=2$: \r\nSubstituting $x=3$ into the second equation, we get $-3+2y=2$, so $2y=5$, which means $y=2.5$. So the point is $(3, 2.5)$.

Step 4: Identify Corner Points of Feasible Region

The corner points of the feasible region are $(3, 3)$, $(3, 4)$, and $(6, 4)$, and $(3, 2.5)$.

Step 5: Evaluate the Objective Function at the Corner Points

We evaluate the objective function $Z = x - 5y$ at each corner point: \r\nAt $(3, 3)$: $Z = 3 - 5(3) = 3 - 15 = -12$ \r\nAt $(3, 4)$: $Z = 3 - 5(4) = 3 - 20 = -17$ \r\nAt $(6, 4)$: $Z = 6 - 5(4) = 6 - 20 = -14$ \r\nAt $(3, 2.5)$: $Z = 3 - 5(2.5) = 3 - 12.5 = -9.5$

Step 6: Determine the Minimum Value

The minimum value of $Z$ is $-17$, which occurs at the point $(3, 4)$.

Final Answer: -17 at (3, 4)

AI generated content. Review strictly for academic accuracy.

Pedagogical Audit
Bloom's Analysis: This is an UNDERSTAND question because the student needs to understand the concepts of linear programming, constraints, feasible region, and how to find the optimal solution graphically. They need to interpret the given constraints and apply them to find the feasible region and then evaluate the objective function at the corner points.
Knowledge Dimension: PROCEDURAL
Justification: The question requires the student to follow a specific procedure to solve the linear programming problem, including graphing the constraints, identifying the feasible region, finding the corner points, and evaluating the objective function.<\/span>
Syllabus Audit: In the context of CBSE Class 12, this is classified as COMPETENCY. The question assesses the student's ability to apply the concepts of linear programming to solve a problem with given constraints, which is a competency-based application of the topic.