SOLUTION: Doreen is a chemist. she needs to prepare 24 ounces of a 7% solution. Find the amount of 12% solution and the amount of a 6% solution she should mix to get this solution? Amount

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Question 417064: Doreen is a chemist. she needs to prepare 24 ounces of a 7% solution. Find the amount of 12% solution and the amount of a 6% solution she should mix to get this solution?
Amount of 12%:
Amount of 6%:

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let a = ounces of 6% solution needed
Let b = ounces of 12% solution needed
--------
given:
(1) a+%2B+b+=+24
(2) +%28.06a+%2B+.12b%29%2F24+=+.07+
---------
.06a+%2B+.12b+=+.07%2A24
.06a+%2B+.12b+=+1.68+
(2) +6a+%2B+12b+=+168+
Multiply both sides of (1) by 6
and subtract from (2)
(2) +6a+%2B+12b+=+168+
(1) -6a+-+6b+=+-144
6b+=+24
b+=+4
and
a+=+24+-+4
a+=+20
She needs 20 ounces of 6% solution and
4 ounces of 12% solution