SOLUTION: A tank holds 80 liters of a chemical solution. Currently, the solution has a strength of 30%. How much of this should be drained and replaced with a 70% solution to get a final str

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Question 98712: A tank holds 80 liters of a chemical solution. Currently, the solution has a strength of 30%. How much of this should be drained and replaced with a 70% solution to get a final strength of 40%?
Answer by ptaylor(2198) About Me  (Show Source):
You can put this solution on YOUR website!
Let x= amount drained and replaced by a 70% solution
Amount of pure chemical remaining after x amount was drained out is 0.30(80-x)
Amount of pure chemical added back in is 0.70x
Amount of pure chemical in the final mixture is 0.40*80
Amount of pure chemical in our solution before they are mixed together=amount of pure chemical after they are mixed so our equation to solve is:
0.30(80-x)+0.70x=0.40*80 get rid of parens
24-0.30x+0.70x=32 subtract 24 from both sides
24-24-0.30x+0.70x=32-24 collect like terms
0.40x=8 divide both sides by 0.40
x=20 liters------------amount drained and replaced by a 70% solution
CK
60*0.30+0.70*20=0.40*80
18+14=32
32=32


Hope this helps---ptaylor