Question 498898
Try this!
Let x = the number of pounds of the 50% corn.  Then the number of pounds of the 90% corn required to make 30 pounds of 80% corn will be (30-x) and, when added together (x+(30-x) = 30) you will get 30 pounds of corn. So we can write an equation to solve for x:
0.5x+0.9(30-x) = 0.8(30) Simplify and solve for x.
0.5x+27-0.9x = 24
-0.4x+27 = 24
-0.4x = -3
x = 7.5
The farmer will need to mix 7.5 pounds of the 50% corn with (30-7.5 = 22.5)pounds of the 90% corn to obtain 30 pounds of 80% corn.