algebra
posted by Jackie .
Soybean meal is 16% protein: cornmeal is 8% protein. How many pounds of each should be mixed together in order to get 320lb. mixture that is 14% protein?

Check the previous answers.
http://www.jiskha.com/search/index.cgi?query=Soybean+Meal+Is+16%25+Protein 
Let x = amount of soybean meal used
y = amount of cormeal used
x + y = 320
.16x + .08y = .15(x + y) = .15(320) = 48
.16x + .08y = 48
That's two equation and two unknowns:
x + y = 320
.16x + .08y = 48
Multiply the first equation by .08:
.08x + .08y = 25.6
.16x + .08y = 48
Subtract the first equation from the second equation:
.16x  .08x + .08y  .08y = 48 = 25.6
.08x = 22.4
Divide by .08:
x = 280
x + y = 320
280 + y = 320
y = 40
Use 280 lbs of soybean meal and 40 lbs of cornmeal.