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

Question 74505: A tank holds 80 liters of a chemical solution. Currently the solution has a strength of 30%. How much of this solution must be drained and replaced with a 70% solution to get a strength of 40%?
Found 2 solutions by stanbon, scott8148:
Answer by stanbon(48558) (Show Source):
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A tank holds 80 liters of a chemical solution. Currently the solution has a strength of 30%. How much of this solution must be drained and replaced with a 70% solution to get a strength of 40%?
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30% solution DATA:
Amt = 80 L ; amt of active ingredient = 0.3*80 = 24 L
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70% solution DATA:
Amt = x L ; amt of active ingredient = 0.7x L
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40% remainder DATA:
Amt = (80) L ; Amt of active ingredient = 0.4(80) = 32 L
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EQUATION:
active - active = active
24 + 0.7x = 32
0.7x = 8
x= 11.43 L
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Cheers,
Stan H.

Answer by scott8148(5891) (Show Source):
You can put this solution on YOUR website!
When the tank is filled with 40% solution, there will be 32 liters of chemical in the solution (40% of 80 liters or .4 X 80). y liters of 30% solution must be drained and replaced with 70% solution.

(chemical left in tank) + (chemical added) = 32 liters

{(80-y) X .30} + (y X .70) = 32

(24-.3y) + .7y = 32

.4y = 8

y = 20 liters