In python 2.x if you divide an int by an int it will round the figure so the output is an int. If you divide an int by a float, even if the output is a whole number the output will be a float.
So given that, all your values are ints and so the output will always be an int and rounded.
Note: should you ever use python 3.x it will automatically output a float if an int divided by another int isn't a whole number.
That should help you, if not this hint from the lesson pretty much tells you exactly what you need to change:
Last but not least, note that (2 + 3) / 2 is not the same as (2 + 3) / 2.0! The former is integer division, meaning Python will try to give you an integer back. You'll want a float, so something like (2 + 3) / 2.0 is the way to go.