I can do the simple stuff, but this is more complicated!

In English, this is what I want to do

If the number in [cell] is <=X then take off %
then
If the number in [cell] is <=Y then take off a further %
then
If the number in [cell] is <=Z then take off a further %
then
Display result

It's probably as nested IF statement, but I don't know how to construct it.

Thanks.