Question 328834
Graph the feasible region.
{{{drawing(300,300,-2,12,-2,12,circle(0,0,.3),circle(0,10,.3),circle(10,10,0.3),circle(10,0,.3),blue(line(0,10,10,10)),blue(line(10.0,10.0,10,0)),grid(1),graph(300,300,-2,12,-2,12,(20-4x)/5))}}}
The area of the triangle is
{{{At=(1/2)(5)(4)=10)}}}
This area is function the region where {{{4x+5y<20}}}.
The area of the square is
{{{As=10*10=100}}}
So the probability that a random point will satisfy {{{4x+5y>=20}}} is equal to 
{{{P=1-At/As=1-10/100=0.9}}}