SOLUTION: How many liters each of 8%, 10%, and 20% hydrogen peroxide should be mixed together to get 8 liters of 12.5% solution, if the amount of 8% solution used must be 2 liters more than

Algebra ->  Customizable Word Problem Solvers  -> Mixtures -> SOLUTION: How many liters each of 8%, 10%, and 20% hydrogen peroxide should be mixed together to get 8 liters of 12.5% solution, if the amount of 8% solution used must be 2 liters more than       Log On

Ad: Over 600 Algebra Word Problems at edhelper.com


   



Question 694580: How many liters each of 8%, 10%, and 20% hydrogen peroxide should be mixed together to get 8 liters of 12.5% solution, if the amount of 8% solution used must be 2 liters more than the amount of 20% solution used?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +a+ = liters of 8% peroxide needed
Let +b+ = liters of 10% peroxide needed
Let +c+ = liters of 20% peroxide needed
-----------
given:
(1) +a+%2B+b+%2B+c+=+8+
(2) +a+=+c+%2B+2+
(3) +%28+.08a+%2B+.1b+%2B+.2c+%29+%2F+8+=+.125+
------------------------------
(3) +.08a+%2B+.1b+%2B+.2c+=+.125%2A8+
(3) +8a+%2B+10b+%2B+20c+=+100+
Multiply both sides of (1) by +10+ and
subtract (1) from (3)
(3) +8a+%2B+10b+%2B+20c+=+100+
(1) +-10a+-+10b+-+10c+=+-80+
+-2a+%2B+10c+=+20+
+-a+%2B+5c+=+10+
----------------
Substitute (2) into this result
+-%28+c+%2B+2+%29+%2B+5c+=+10+
+-c+-+2+%2B+5c+=+10+
+4c+=+12+
+c+=+3+
and, since
(2) +a+=+c+%2B+2+
(2) +a+=+3+%2B+2+
(2) +a+=+5+
and
(1) +5+%2B+b+%2B+3+=+8+
(1) +b+=+8+-+8+
(1) +b+=+0+
5 liters of 8% peroxide is needed
No 10% peroxide is needed
3 liters of 20% peroxide is needed
-----------------------------
Check answer:
(3) +%28+.08a+%2B+.1b+%2B+.2c+%29+%2F+8+=+.125+
(3) +%28+.08%2A5+%2B+.1%2A0+%2B+.2%2A3+%29+%2F+8+=+.125+
(3) +%28+.4+%2B+0+%2B+.6+%29+%2F+8+=+.125+
(3) +1+=+.125%2A8+
(3) +1+=+1+
OK