SOLUTION: A pharmasist needs 500 milliliters of a 20% phenobarbital solution. But has only 5% and 25% phenobarbital solutions available. Find how many milliliters of each he should mix to

Question 126663: A pharmasist needs 500 milliliters of a 20% phenobarbital solution. But has only 5% and 25% phenobarbital solutions available. Find how many milliliters of each he should mix to get the desired solution.
Found 2 solutions by edjones, josmiceli:
Answer by edjones(8007) (Show Source): You can put this solution on YOUR website!
Let x be ml of 5% soln.
let 500-x be ml of 25% soln.
.
x*.05=.05x
(500-x)*.25=125-.25x
500*.20=100
.
.05x+125-.25x=100
-.2x=-25
x=-25/-.2
x=125 ml of 5% soln.
500-x=375 ml of 25% soln.
.
Check:
125*.05= 6.25
375*.25=93.75
---------------
========100
.
Ed
Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!

He needs 375 ml of the 25% solution and 125 ml of the 5% solution
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