Soymeal is 14 percent protein cornmeal is 7 percent protein how many pounds of each should be mixed together in order to get 280-lb mixture that is 9 percent protein

Let the weight of soymeal be s, and let the weight of cornmeal be c.
You need a total of 280 lb, so that gives us one equation.

s + c = 280

Now we use the protein to write another equation.
The protein in s lb of soymeal is 0.14s.
The protein in c lb of cornmeal is 0.07c.
The protein in 280 lb of 0.09% protein mix is 0.09(280).
This gives us a second equation.

0.14s + 0.07c = 0.09(280)

Now we solve the two equations as a system of equations.

s + c = 280
0.14s + 0.07c = 0.09(280)

Solve the first equation for s and plug in tot eh second equation.

s = 280 - c

0.14(280 - c) + 0.07c = 25.2

39.2 - 0.14c + 0.07c = 25.2

-0.07c = -14

c = 200

Now we substitute c = 200 in the first equation to find s.

s + 200 = 280

s = 80

200 lb of soymeal and 80 lb of cornmeal