SOLUTION: Solution A is 50% alcohol. Solution B is 20% alcohol. We want to create a 20 liter mixture of the two solutions that will be 32% alcohol. How many liters of each solution should be

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Question 495507: Solution A is 50% alcohol. Solution B is 20% alcohol. We want to create a 20 liter mixture of the two solutions that will be 32% alcohol. How many liters of each solution should be used?
Found 2 solutions by josmiceli, Earlsdon:
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let a = liters of solution A needed
Let b = liters of solution B needed
given:
(1) +a+%2B+b+=+20+
(2) +.5a+%2B+.2b+=+.32%2A20+
---------------------
(2) +.5a+%2B+.2b+=+6.4+
(2) +5a+%2B+2b+=+64+
Multiply both sides of (1) by 2
and subtract (1) from (2)
(2) +5a+%2B+2b+=+64+
(1) +-2a+-+2b+=+-40+
+3a+=+24+
+a+=+8+
and, since,
(1) +a+%2B+b+=+20+
(1) +b+=+20+-+8+
(1) +b+=+12+
8 liters of solution A are needed
12 liters of solution B are needed
check answer:
(2) +.5a+%2B+.2b+=+6.4+
(2) +.5%2A8+%2B+.2%2A12+=+6.4+
(2) +4+%2B+2.4+=+6.4+
(2) +6.4+=+6.4+
OK

Answer by Earlsdon(6294) About Me  (Show Source):
You can put this solution on YOUR website!
Let x = the required number of liters of solution A (50% alcohol solution), then (20-x) will be the number of liters of solution B (20% alcohol solution).
The sum of these is to be 20 liters of 32% alcohol solution.
This situation can be expressed (after changing the percentages to their decimal equivalents) in the following equation:
0.5x%2B0.20%2820-x%29+=+0.32%2820%29 Simplify and solve for x.
0.5x%2B4-0.2x+=+6.4 Combine the x-terms.
0.3x%2B4+=+6.4 Subtract 4 from both sides.
0.3x+=+2.4 Finally, divide both sides by 0.3
x+=+8liters and...
20-x+=+12liters.
You will need to mix 8 liters of solution A (the 50% alcohol solution) with 12 liters of solution B (the 20% alcohol solution) to obtain 20 liters of 32% alcohol solution.