You can perform almost any arithmetic operation that you can think of plus, minus, square root e.t.c. When you perform arithmetic it would be pretty pointless to do it on simple numbers that don't change and also to not store the result.
To avoid this most arithmetic is performed on and stored in variables as covered earlier. To see a few examples of what can take place simply click somewhere on this page, after seeing the page take a look at the page source of this file as it will reveal