SOLUTION: A flask contains 500 ml of an 80% alcohol solution in water. How much of this solution must be drawn off and replaced by water to obtain a solution having a concentration of 25% al
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Question 768499: A flask contains 500 ml of an 80% alcohol solution in water. How much of this solution must be drawn off and replaced by water to obtain a solution having a concentration of 25% alcohol?
what are the steps to solve this problem? i get confused when there are already situations where you have to replace and to draw off things in the problem. Thankyou :)
Answer by josgarithmetic(39618) (Show Source): You can put this solution on YOUR website!
This calculation will be simpler than if you were replacing the solution with a different concentration of alcohol solution.
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You begin with a liquid of 500 ml. volume, and you finish with a liquid of 500 ml. volume. When you perform the replacement with the water, you are adding NO alcohol.
Let v = volume in milliliters to remove, before replacing with the v of water.
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This is using decimal fractions, being my attempt to make this seem less confusing (maybe it works, maybe not).
The equation is in this case, perfectly equivalent to
or if desired, equivalent to
SOLVE FOR v.
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Do the arithmetic and find v = 343.75 ml. but in practice it should really be 343 or 344.
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