SOLUTION: Alyssa is a chemist with Gemco Pharmaceutical Company. She needs to prepare 12 ounces of a 9% hydrochloric acid solution. The only solutions she currently has available are 4% a

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Question 515168: Alyssa is a chemist with Gemco Pharmaceutical Company. She needs to prepare 12 ounces of a 9% hydrochloric acid solution. The only solutions she currently has available are 4% and 12% hydrochloric acid. How much should she use of each solution to obtain the needed solution? Use variables and representation if possible.
Found 2 solutions by josmiceli, lwsshak3:
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let a = ounces of 4% solution needed
Let b = ounces of 12% solution needed
given:
(1) +a+%2B+b+=+12+
(2) +%28+.04a+%2B+.12b+%29+%2F+12+=+.09+
--------------------------
(2) +.04a+%2B+.12b+=+.09%2A12+
(2) +.04a+%2B+.12b+=+1.08+
(2) +4a+%2B+12b+=+108+
Multiply both sides of (1) by 4
and subtract (1) from (2)
(2) +4a+%2B+12b+=+108+
(1) +-4a+-+4b+=+-48+
+8b+=+60+
+b+=+7.5+
and, since
(1) +a+%2B+b+=+12+
(1) +a+=+12+-+7.5+
(1) +a+=+4.5+
4.5 ounces of 4% solution are needed
7.5 ounces of 12% solution are needed

Answer by lwsshak3(11628) About Me  (Show Source):
You can put this solution on YOUR website!
Alyssa is a chemist with Gemco Pharmaceutical Company. She needs to prepare 12 ounces of a 9% hydrochloric acid solution. The only solutions she currently has available are 4% and 12% hydrochloric acid. How much should she use of each solution to obtain the needed solution? Use variables and representation if possible.
**
let x=ounces of 4% solution
12-x=ounces of 12% solution
..
4%x+12%(12-x)=9%*12
.04x+1.44-.12x=.09*12
-.08x=-.36
x=.36/.08
4=4.5 ounces
ans:
Alyssa should use of each of the following solutions to obtain the needed solution
4.5 ounces of 4% solution
and
7.5 ounces of 12% solution