Here is the general concept.

I have 56 Televisions. The month is currently april and 3 of those 56 have
failed(quit, don't work). I am wanting to try and find a quick and easy
formula that gives me the rate of failure. I know it is probably something
simple, though it seems all brain power has left me on a friday.

56 Television
3 Quit
4 Months into the year
Televisions are 1997 or older
2 different kinds -- Magnavox and Phillips.

I have a spreadsheet all laid out, though I just can't seem to think of the
way to tie it all together. I would like to show the rate of failure between
the two brands as well. 2 of those 3 are Magnavox's, and the other 1 is
Phillips. Any help would be -greatly- appreciated!

Thanks ahead of time!