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Consider the following L.L.P.

Minimize z = 30x - 30y + 1800;

subject to x + y ≤ 30, x ≤ 15, y ≤ 20, x + y ≥ 15 and x, y ≥ 0.

Then it attains its optimal value at the point

Solution

Correct Option: 1

The objective function to minimize is:

z=30x30y+1800z = 30x - 30y + 1800

Subject to constraints:

  • x+y30x + y \leq 30
  • x15x \leq 15
  • y20y \leq 20
  • x+y15x + y \geq 15
  • x,y0x, y \geq 0

The corner points of the feasible region are found by intersecting the constraint lines:

At x=0x = 0 and x+y=15x + y = 15:

y=15y = 15

Point: (0,15)(0, 15)

At x=0x = 0 and y=20y = 20:

Point: (0,20)(0, 20)

At y=20y = 20 and x+y=30x + y = 30:

x+20=30x + 20 = 30

x=10x = 10

Point: (10,20)(10, 20)

At x=15x = 15 and x+y=30x + y = 30:

15+y=3015 + y = 30

y=15y = 15

Point: (15,15)(15, 15)

At x=15x = 15 and x+y=15x + y = 15:

15+y=1515 + y = 15

y=0y = 0

Point: (15,0)(15, 0)


Evaluating z=30x30y+1800z = 30x - 30y + 1800 at each corner point:

At (0,15)(0, 15):

z=30(0)30(15)+1800z = 30(0) - 30(15) + 1800

z=0450+1800z = 0 - 450 + 1800

z=1350z = 1350

At (0,20)(0, 20):

z=30(0)30(20)+1800z = 30(0) - 30(20) + 1800

z=0600+1800z = 0 - 600 + 1800

z=1200z = 1200

At (10,20)(10, 20):

z=30(10)30(20)+1800z = 30(10) - 30(20) + 1800

z=300600+1800z = 300 - 600 + 1800

z=1500z = 1500

At (15,15)(15, 15):

z=30(15)30(15)+1800z = 30(15) - 30(15) + 1800

z=450450+1800z = 450 - 450 + 1800

z=1800z = 1800

At (15,0)(15, 0):

z=30(15)30(0)+1800z = 30(15) - 30(0) + 1800

z=4500+1800z = 450 - 0 + 1800

z=2250z = 2250


The minimum value is z=1200z = 1200 at point (0,20)(0, 20).

Therefore, the optimal value is attained at (0,20)(0, 20).

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