Solution X is 10 percent alcohol by volume, and solution Y is 30 percent alcohol by volume. How many milliliters of solution Y must be added to 200 milliliters of solution X to create a solution that is 20 percent alcohol by volume? Answers
A) 200  B) 300  C) 400  D) 500  E) 600
20% is an equal distance between 10% and 30%.   Thus there should be equal parts of both solutions.   We should add 200 ml of solution Y.   The answer is 200.
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Solution X is 10 percent alcohol by volume, and solution Y is 30 percent alcohol by volume. How many milliliters of solution Y must be added to 200 milliliters of solution X to create a solution that is 20 percent alcohol by volume?