SOLUTION: How much 30% alcohol, 45% alcohol, 60% alcohol and 95% alcohol could be mixed to make 20ml of 50% alcohol? Who helps me

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Question 921829: How much 30% alcohol, 45% alcohol, 60% alcohol and 95% alcohol could be mixed to make 20ml of 50% alcohol?
Who helps me

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +a+ = ml of 30% alcohol
Let +b+ = ml of 45% alcohol
Let +c+ = ml of 60% alcohol
Let +d+ = ml of 95% alcohol
+.5%2A20+=+10+ ml of alcohol in final mixture
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+a+%2B+b+%2B+c+%2B+d+=+20+
+.3a+%2B+.45b+%2B+.6c+%2B+.95d+=+10+
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Actually you don't need any 95% or 30%
so, I can say:
(1) +b+%2B+c+=+20+
(2) +.45b+%2B+.6c+=+10+
(2) +45b+%2B+60c+=+1000+
(2) +9b+%2B+12c+=+200+
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Multiply both sides of (1) by +9+ and
subtract (1) from (2)
(2) +9b+%2B+12c+=+200+
(1) +-9b+-+9c+=+-180+
+3c+=+20+
+c+=+6.667+
and
(1) +b+%2B+c+=+20+
(2) +b+=+20+-+6.667+
(2) +b+=+13.333+
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0 ml of 30% alcohol
13.333 ml of 45% alcohol
6.667 ml of 60% alcohol
0 ml of 95% alcohol
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Hope I got it