Antifreeze Mixtures

[yd3@nvc.net]

Greetings from cold South Dakota.

A few days ago I conducted an experiment on what happens to weak
antifreeze mixures when they freeze.

I made up two 500 mL concentrations: 25% antifreeze and 33% antifreeze. 
Now that I am done I wanted to increase each one to 50% antifreeze so I
can use it in my leaky truck.  How much antifreeze should I have added
to each one to get each mixure back up to 50%?

Regards, 
Blake