SOLUTION: you have a 70% alcohol solution and a 20% alcohol solution and want to make 20 ounces of a 50% soultion by mixing the two. How many ounces of the 70% soultion would u use?

Algebra ->  Customizable Word Problem Solvers  -> Mixtures -> SOLUTION: you have a 70% alcohol solution and a 20% alcohol solution and want to make 20 ounces of a 50% soultion by mixing the two. How many ounces of the 70% soultion would u use?      Log On

Ad: Over 600 Algebra Word Problems at edhelper.com


   



Question 544050: you have a 70% alcohol solution and a 20% alcohol solution and want to make 20 ounces of a 50% soultion by mixing the two. How many ounces of the 70% soultion would u use?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let a = ounces of 70% solution needed
Let b = ounces of 20% solution needed
given:
+.7a+ = alcohol in 70% solution
+.2b+ = alcohol in 20% solution
-----------------------------
In words:
( ounces of alcohol in 70% and 20% solutions) / ( ounces in final mixture ) = 50%
given:
(1) +a+%2B+b+=+20+
(2) +%28+.7a+%2B+.2b+%29+%2F+20+=+.5+
----------------------
(2) +.7a+%2B+.2b+=+10+
(2) +7a+%2B+2b+=+100+
Multiply both sides of (1) by 2
and subtract (1) from (2)
(2) +7a+%2B+2b+=+100+
(1) +-2a+-+2b+=+-40+
+5a+=+60+
+a+=+12+
and, since
(1) +a+%2B+b+=+20+
(1) +12+%2B+b+=+20+
(1) +b+=+8+
12 ounces of 70% solution and 8 ounces of 20% solution are needed
check answer:
(2) +%28+.7a+%2B+.2b+%29+%2F+20+=+.5+
(2) +%28+.7%2A12+%2B+.2%2A8+%29+%2F+20+=+.5+
(2) +%28+8.4+%2B+1.6+%29+%2F+20+=+.5+
(2) +10%2F20+=+.5+
OK