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?  Choices
A) 200
B) 300
C) 400
D) 500
E) 600

Rationale: "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 a ."
Answer: A