For the LPP: minimize z=6x+3y subject to the constraints:
4x+y≥80
x+5y≥115
3x+2y≤150
x≥0,y≥0
The minimum value occurs at a corner point of the feasible region.
Finding the intersection of 4x+y=80 and x+5y=115:
y=80−4x
x+5(80−4x)=115
x+400−20x=115
−19x=−285
x=15
y=80−4(15)
y=20
Corner point: (15,20)
Finding the intersection of 4x+y=80 and 3x+2y=150:
y=80−4x
3x+2(80−4x)=150
3x+160−8x=150
−5x=−10
x=2
y=80−4(2)
y=72
Corner point: (2,72)
Finding the intersection of x+5y=115 and 3x+2y=150:
x=115−5y
3(115−5y)+2y=150
345−15y+2y=150
−13y=−195
y=15
x=115−5(15)
x=40
Corner point: (40,15)
Evaluating z=6x+3y at each corner point:
At (15,20):
z=6(15)+3(20)
z=90+60
z=150
At (2,72):
z=6(2)+3(72)
z=12+216
z=228
At (40,15):
z=6(40)+3(15)
z=240+45
z=285
The minimum value of z is 150 at point (15,20).