[Tutor] my first program

[Caughell family]

This is a little program I designed to test experimental odds against
theoretical odds.

There is a problem.

After much deliberation, I simplified the formula that I was using to make
the differentiation percentage with, which ended up doing the exact same
thing, just simpler.  However, the program still wouldn't work.  

The problem is that I don't know how to make a division become a real
number, especially when involving variables.  (I know that I can do 2/7.0
instead of 2/7 to make it a real result)

Thanks a lot!

Also, I've got one question involving real numbers in this python..  
is there any way that I can limit the number to a certain ammount of decimal
places?  will it be rounded or truncated, or automatically rounded up?

Thanks very much!!!