Some of the 50% solution of acid was removed and this was replaced with an equal amount of 10% solution of acid. As a result, a 20% solution of acid was obtained. What fraction of the original solution was replaced? Choose the correct choice from the following:  A) 1/2  B) 2/3  C) 3/4  D) 3/5  E) 4/5
Let x be the fraction of the original solution that was replaced.   0.5*(1-x)+0.1(x)=0.2   0.4x=0.3   x=3/4   The answer is 3/4.
<result>C</result>
Some of the 50% solution of acid was removed and this was replaced with an equal amount of 10% solution of acid. As a result, a 20% solution of acid was obtained. What fraction of the original solution was replaced?