A certain quantity of 50% solution is replaced with 25% solution such that the new concentration is 35%. What is the fraction of the solution that was replaced?  Choose the correct choice from the following choices
A) 1/4  B) 1/3  C) 1/2  D) 2/3  E) 3/5
Let's say that the total original mixture A is 100 ml   The original mixture A thus has 50 ml of alcohol out of 100 ml of solution   You want to replace some of that original mixture A with another mixture B that contains 25 ml of alcohol per 100 ml. Thus, the difference between 50 ml and 25 ml is 25 ml per 100 ml of mixture. This means that every time you replace 100 ml of the original mixture A by 100 ml of mixture B, the original alcohol concentration will decrease by 25%. The question says that the new mixture, let's call it C, must be 35% alcohol, a decrease of only 15%. Therefore, 15 out of 25 is 3/5 and 3/5 is the answer.
<result>E</result>
A certain quantity of 50% solution is replaced with 25% solution such that the new concentration is 35%. What is the fraction of the solution that was replaced?