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For the objective function Z=3x+5yZ = 3x + 5y subject to constraints x+3y≥3x + 3y \geq 3, x+y≥2x + y \geq 2, x≥0x \geq 0, y≥0y \geq 0:

Solution

✅ Correct Option: 2

Objective function: Z=3x+5yZ = 3x + 5y

Constraints:

  • x+3y≥3x + 3y \geq 3
  • x+y≥2x + y \geq 2
  • x≥0x \geq 0
  • y≥0y \geq 0

The constraints use ≥\geq signs, indicating the feasible region is above/right of the boundary lines.


Finding the corner points where constraint lines intersect:

Intersection of x+3y=3x + 3y = 3 and x+y=2x + y = 2:

From x+y=2x + y = 2:

x=2−yx = 2 - y

Substituting into x+3y=3x + 3y = 3:

(2−y)+3y=3(2 - y) + 3y = 3

2+2y=32 + 2y = 3

2y=12y = 1

y=0.5y = 0.5

x=2−0.5=1.5x = 2 - 0.5 = 1.5

Point A: (1.5,0.5)(1.5, 0.5)


Intersection of x+3y=3x + 3y = 3 and y=0y = 0:

x+3(0)=3x + 3(0) = 3

x=3x = 3

Point B: (3,0)(3, 0)


Intersection of x+y=2x + y = 2 and x=0x = 0:

0+y=20 + y = 2

y=2y = 2

Point C: (0,2)(0, 2)


Since all constraints use ≥\geq and the feasible region extends infinitely upward and to the right, the region is unbounded.

The objective function Z=3x+5yZ = 3x + 5y has positive coefficients. As xx or yy increase, ZZ increases.

In an unbounded region where both variables can increase indefinitely, ZZ has no maximum value.


Evaluating Z=3x+5yZ = 3x + 5y at each corner point:

At point A (1.5,0.5)(1.5, 0.5):

Z=3(1.5)+5(0.5)Z = 3(1.5) + 5(0.5)

Z=4.5+2.5Z = 4.5 + 2.5

Z=7Z = 7

At point B (3,0)(3, 0):

Z=3(3)+5(0)Z = 3(3) + 5(0)

Z=9Z = 9

At point C (0,2)(0, 2):

Z=3(0)+5(2)Z = 3(0) + 5(2)

Z=10Z = 10

The minimum value is Z=7Z = 7 at point (1.5,0.5)(1.5, 0.5).


Therefore, there exists only a minimum value of ZZ.

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