I have pure ethanol and water. When mixed, the total volume is not the sum of the individual volumes (its a little bit less). A wikipedia graph has shown that a 0.4mol ethanol to 0.6mol to water mixture is ideal to get the most contraction. (http://upload.wikimedia.org/wikipedia/commons/4/45/Excess_Volume_Mixture_of_Ethanol_and_Water.png)
How do I calculate how much ethanol and water to add if I needed to get 100ml of solution with the mole ratio is 0.4 ethanol to 0.6 water.
The Attempt at a Solution
I honestly don't know what to do, I just need hints or something because trying to get my heard around this concept in making my head hurt