Methods from C Pine book -- need some help understanding the basic concepts

Newbie question. I’m using C Pine’s great book on Intro to Programming
with Ruby and am stuck on the code in ch8 and I do not get it at all…
the code and my comments or where I get stuck are here:
http://codepad.org/rjhEy2eg

In Ruby, any standard mathematics involving two Integers will result an
an Integer unless you specifically alter one of the operands to a Float
(or something else).

It works because according to those rules:

3 / 10 = 0

3.0 / 10 = 0.3

3.to_f / 10 = 0.3

So in the operations performed, he’s relying on the way Integers (Fixnum
Class) behave.