SOLUTION: needs to prepare 28 ounces of a 9% hydrochloric acid solution. find the amount of 14% solution and the amount of 7% solution she should mix. how many ounces of the 14% acid solutio

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Question 1078772: needs to prepare 28 ounces of a 9% hydrochloric acid solution. find the amount of 14% solution and the amount of 7% solution she should mix. how many ounces of the 14% acid solution should be in the mixture?
Found 2 solutions by stanbon, Edwin McCravy:
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
needs to prepare 28 ounces of a 9% hydrochloric acid solution. find the amount of 14% solution and the amount of 7% solution she should mix. how many ounces of the 14% acid solution should be in the mixture?
Equation:
acid + acid = acid
------
0.14x + 0.07(28-x) = 0.09*28
--------------------------------
14x + 7*28 - 7x = 9*28
----
7x = 2*28
x = 8 ounces (amt. of 14% solution needed)
28-x = 20 ounces (amt. of 7% solution needed)
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Cheers,
Stan H.
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Answer by Edwin McCravy(20056) About Me  (Show Source):
You can put this solution on YOUR website!
I think you should use 2 unknowns:



Get rid of the decimals by moving them all 2 places to the right:



Now we can divide the second equation through by 7





Multiply the first equation through by -1
to eliminate the y's



matrix%281%2C7%2C%0D%0A%0D%0Ax%2C%22%22%2C%22%22%2C%22%22%2C%22%22=%22%22%2C%22%22%2C8%29

So we must use 8 ounces of the 14% 

Substitute x = 8 in 





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And we must use 20 ounces of the 7%.

Edwin