SOLUTION: One solution contains 50% alcohol and another solution contains 80% alcohol. How many liters of each solution should be mixed to produce 10.5 liters of a 70% alcohol solution? How

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Question 486933: One solution contains 50% alcohol and another solution contains 80% alcohol. How many liters of each solution should be mixed to produce 10.5 liters of a 70% alcohol solution? How do i work this out?
Found 2 solutions by John10, josmiceli:
Answer by John10(297) About Me  (Show Source):
You can put this solution on YOUR website!
Hint: it is good to draw a picture.
First, you call x to be the amount of 50% alcohol
y---------------------80%-------
The total is 10.5 L
x + y = 10.5 (1)
The mixture is:
0.5x + 0.8y = 10.5(0.70) = 7.5 (2)
Solve (1) and (2) to find the amount of each solution.
John10:)

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let a = liters of 50% alcohol solution needed
Let b = liters of 80% alcohol solution needed
given:
(1) +a+%2B+b+=+10.5+
+.5a+ = liters of alcohol in the 50% alcohol solution
+.8b+ = liters of alcohol in the 80% alcohol solution
(2) +%28.5a+%2B+.8b%29+%2F+10.5+=+.7+
------------------------
From (2):
(2) +.5a+%2B+.8b+=+.7%2A10.5+
(2) +.5a+%2B+.8b+=+7.35+
(2) +50a+%2B+80b+=+735+
Multiply both sides of (1) by 50 and
subtract (1) from (2)
(2) +50a+%2B+80b+=+735+
(1) +-50a+-+50b+=+525+
+30b+=+210+
+b+=+7+
and, from (1),
(1) +a+%2B+b+=++10.5+
(1) +a+%2B+7+=+10.5+
(1) +a+=+3.5+
3.5 liters of 50% alcohol solution are needed
7 liters of 80% alcohol solution are needed
check answer:
(2) +%28.5a+%2B+.8b%29+%2F+10.5+=+.7+
(2) +%28.5%2A3.5+%2B+.8%2A7%29+%2F+10.5+=+.7+
(2) +%281.75+%2B+5.6%29+.+10.5+=+.7+
(2) +7.35%2F10.5+=+.7+
(2) +7.35+=+7.35+
OK