SOLUTION: A chemist has one solution that is 20% acid and a second that is 65% acid. How many gallons of each should be mixed together to get 120 gallons of a solution that is 50% acid?

Algebra ->  Customizable Word Problem Solvers  -> Mixtures -> SOLUTION: A chemist has one solution that is 20% acid and a second that is 65% acid. How many gallons of each should be mixed together to get 120 gallons of a solution that is 50% acid?      Log On

Ad: Over 600 Algebra Word Problems at edhelper.com


   



Question 551101: A chemist has one solution that is 20% acid and a second that is 65% acid. How many gallons of each should be mixed together to get 120 gallons of a solution that is 50% acid?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +a+ = gallons of 20% solution needed
Let +b+ = gallons of 65% solution needed
+.2a+ = gallons of acid in 20% solution
+.65b+ = gallons of acid in 65% solution
given:
(1) +a+%2B+b+=120+
(2) +%28+.2a+%2B+.65b+%29+%2F+120+=+.5+
-------------------------
(2) +.2a+%2B+.65b+=+.5%2A120+
(2) +.2a+%2B+.65b+=+60+
(2) +20a+%2B+65b+=+6000+
Multiply both sides of (1) by +20+
and subtract (1) from (2)
(2) +20a+%2B+65b+=+6000+
(1) +-20a+-+20b+=+-2400+
+45b+=+3600+
+b+=+80+
and, since
(1) +a+%2B+b+=120+
(1) +a+%2B+80+=120+
(1) +a+=+120+-+80+
(1) +a+=+40+
40 gallons of 20% solution are needed
80 gallons of 65% solution are needed
check answer:
(2) +%28+.2%2A40+%2B+.65%2A80+%29+%2F+120+=+.5+
(2) +%28+8+%2B+52+%29+%2F+120++=+.5+
(2) +60+%2F+120+=+.5+
(2) +60+=+.5%2A120+
(2) +60+=+60+
OK