Question

Use graphical method
Minimize: $z=600x+900y$
Subject to:
$40x+60y\ge 480$
$30x+15y\ge 180$
$x\ge 0,y\ge 0$

Answer 1

If we let $z=Rs.8100$, then:
$8100=600x+900y,(x=0,y=9)(x=13.5,y=0)$
The resultant trial cost is shown in the figure.
The line is parallel to the boundary line BC. The lowest acceptable cost solution will be coincidental with the line BC making point B, point C and any other points on the line BC optical. Multiple optimum solutions present the manager with choice and hence some flexibility