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Which one of the following inequalities is redundant for the shaded feasible region (ABCDA) shown below?

Figure for CUET Mathematics 2025 19 May Shift 1 question 4 (Algebra)

Solution

✅ Correct Option: 3

A redundant constraint is an unnecessary rule that doesn't form any boundary of the feasible region. Even if removed, the shaded region stays exactly the same.


The four constraints are:

  1. x+2y≤40x + 2y \leq 40
  2. 3x+y≥303x + y \geq 30
  3. 4x+3y≤604x + 3y \leq 60
  4. x≥0,y≥0x \geq 0, y \geq 0

The feasible region is ABCDA with vertices A, B, C, D.


The boundary lines are:

Line 1: x+2y=40x + 2y = 40

Line 2: 3x+y=303x + y = 30

Line 3: 4x+3y=604x + 3y = 60

Lines 4: x=0x = 0 and y=0y = 0


Point A (Line 2 meets y-axis):

Put x=0x = 0 in 3x+y=303x + y = 30

y=30y = 30

Point A =(0,30)= (0, 30)


Point B (Line 1 meets Line 2):

x+2y=40x + 2y = 40

3x+y=303x + y = 30

From the second equation: y=30−3xy = 30 - 3x

Substituting into the first equation:

x+2(30−3x)=40x + 2(30 - 3x) = 40

x+60−6x=40x + 60 - 6x = 40

−5x=−20-5x = -20

x=4x = 4

y=30−12=18y = 30 - 12 = 18

Point B =(4,18)= (4, 18)


Point C (Line 1 meets x-axis):

Put y=0y = 0 in x+2y=40x + 2y = 40

x=40x = 40

Point C =(40,0)= (40, 0)


Point D (Line 2 meets x-axis):

Put y=0y = 0 in 3x+y=303x + y = 30

x=10x = 10

Point D =(10,0)= (10, 0)


Checking if 4x+3y=604x + 3y = 60 passes through any vertex:

At A (0,30)(0, 30): 4(0)+3(30)=90≠604(0) + 3(30) = 90 \neq 60

At B (4,18)(4, 18): 4(4)+3(18)=70≠604(4) + 3(18) = 70 \neq 60

At C (40,0)(40, 0): 4(40)+3(0)=160≠604(40) + 3(0) = 160 \neq 60

At D (10,0)(10, 0): 4(10)+3(0)=40≠604(10) + 3(0) = 40 \neq 60

Constraint 3 doesn't form any edge of the feasible region.


The feasible region ABCDA is completely defined by constraints 1, 2, and 4. Constraint 3 plays no role in forming the boundaries.

Therefore, the inequality 4x+3y≤604x + 3y \leq 60 is redundant.

The answer is Option 3.

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