Question 1128980
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You already have three good responses to your question, all of them involving a moderately complicated algebraic equation.<br>
Here is a MUCH faster and easier way to solve a "mixture" problem like this.<br>
(1) You are adding 100% alcohol to 25% alcohol; you want to end up with 40% alcohol.
(2) 40% is 1/5 of the way from 25% to 100%.  (40-25 = 15; 100-25 = 75; 15/75 = 1/5)
(3) That means 1/5 of the mixture should be the 100% alcohol that you are adding.<br>
1/5 of the 2.5L capacity of the container is 0.5L.<br>
ANSWER: 0.5L of the 25% alcohol should be drained and replaced with 100% alcohol to get 2.5L of 40% alcohol.