Question

if soybean is 15% protein,cornmeal is 7%protein, how many pounds of each should be mixed together to get 280 pounds that is 8 % protein

Answer 1

You want a total of 22.4 pounds of protein, if you want 280 pounds at 8% protein.

Let s = pounds of soybean, and c = pounds of cornmeal.

You want s + c = 280.

You also want the percentages to equal 8%, or 22.4 pounds:

.15s + .07 c = 22.4

So you solve the two equations
s+c=280 and
.15s+.07c=22.4

You can use substitution, as that will probably be the fastest