SOLUTION: Soybean meal is 12% protein, cornmeal is 6 % protein. How many punds of each should be mixed together in order to get 240lb mixture that is 9% protein. Ive been stuck on this pro

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Question 175992: Soybean meal is 12% protein, cornmeal is 6 % protein. How many punds of each should be mixed together in order to get 240lb mixture that is 9% protein. Ive been stuck on this problem for 2 days. i cannot even vizualize it. I am sitting with my daughter at the hospital for 3 days now, and some of my worries of her are probably getting in my way, but this problem just is not getting past me reading and re reading it. We did one similar to this, just different numbers several weeks ago, but I just cant even get started. can you help me?
Answer by Mathtut(3670) About Me  (Show Source):
You can put this solution on YOUR website!
I am so sorry to hear that you daughter is in the hospital. My prayers go out to you.
:
lets call x and y the amounts of 12% and 6% mixtures respectively.
:
x+y=240...............eq 1
.12x+.06y=.09(240)....eq 2
:
rewrite eq 1 to x=240-y and plug x's value into eq 2
:
.12(240-y)+.06y=21.6
:
28.8-.12y+.06y=21.6
:
-.06y=7.2
:
highlight%28y=120%29pounds of 6% protein
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highlight%28x=240-120=120%29pounds of 12% protein
:
this all makes sense because 9% is 1/2 way in between 6% and 12% so we use equal amounts of both.