SOLUTION: Soybean is 18% protein Cornmeal is 9% protein How many lbs of each should be mixed together to get 360-lb mixture that is 12% protein?

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Question 436332: Soybean is 18% protein
Cornmeal is 9% protein
How many lbs of each should be mixed together to get 360-lb mixture that is 12% protein?

Found 3 solutions by stanbon, htmentor, josmiceli:
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
Soybean is 18% protein
Cornmeal is 9% protein
How many lbs of each should be mixed together to get 360-lb mixture that is 12% protein?
----
Equations:
Quantity Eq: s + c = 360 lb
Protein Eq:0.18s+0.09c = 0.12(360)
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Multiply thru the 1st by 18
Multiply thru the 2nd by 100
--------------------------------
18s + 18c = 18*360
18x + 9c = 12*360
----------------------
Subtract and solve for "c":
9c = 6*360
c = (2/3)360
c = 240 lb. (amt. of cornmeal needed)
===============
Solve for "s":
s + c = 360
s + 240 = 360
s = 120 lb (amt of soybean needed)
======================================
Cheers,
Stan H.
===============

Answer by htmentor(1343) About Me  (Show Source):
You can put this solution on YOUR website!
Let x = the number of pounds of soybeans
Then 360-x = the number of pounds of cornmeal
A 360 lb. 12% mixture contains 0.12*360 = 43.2 lb
So we can write the following equation:
0.18x + 0.09(360-x) = 43.2
Solve for x:
0.09x = 43.2 - 32.4 = 10.8 -> x = 120
So the number of lbs of soybeans = 120
And the number of lbs of cornmeal = 360-120 = 240

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let a = pounds of soybean needed
Let b = pounds of cornmeal needed
given:
+.18a+ = protein in soybeans
+.09b+ = protein in cornmeal
(1) +a+%2B+b+=+360+
(2) %28++.18a+%2B+.09b+%29%2F360+=+.12+
-----------------------
(2) %28++.18a+%2B+.09b+%29%2F360+=+.12+
(2) ++.18a+%2B+.09b++=+.12%2A360+
(2) ++.18a+%2B+.09b++=+43.2+
(2) ++18a+%2B+9b++=+4320+
Multiply both sides of (1) by 9 and
subtract (1) from (2)
(2) ++18a+%2B+9b++=+4320+
(1) +-9a+-+9b+=+-3240+
+9a+=+1080+
+a+=+120+
and
(1) +120+%2B+b+=+360+
+b+=+240+
120 pounds of soybeans are needed
240 pounds of cornmeal are needed
check answer:
(2) %28++.18%2A120+%2B+.09%2A240+%29%2F360+=+.12+
(2) %28++21.6+%2B+21.6+%29%2F360+=+.12+
(2) +43.2%2F360+=+.12+
+43.2+=+.12%2A360+
+43.2+=+43.2+
OK