I am not sure how to break this question down

Question

How many quarts of pure antifreeze must be added to 5 quarts of a 20​% antifreeze solution to obtain a 30​% antifreeze​ solution?

Answer 1

I'm assuming that it is supposed to be worded like this: A solution, which is 20% anti-freeze, is 5 quarts. You need to add x quarts, which are 100% anti-freeze, to get the entire solution to be 30% anti-freeze. Find x.

1. Set up a ratio: 0.20/5 = 0.30/x
2. Cross multiply: 0.20x = 1.5
3. Solve for x: x = 7.5
4. However, because there was already 5 quarts, which made up the 20%, the 7.5 quarts that makes up 30% means that the number of quarts actually needed of pure anti-freeze is 2.5