Use this diagram, it might help.
From the inside, whatever that layer is, it can be any of the layers outside of it.
All whole numbers can be a rational number, but not all rational numbers be a whole number.
Kind of like all squares can be rectangles, but not all rectangles can be a square.
The whole number has all the attributes of a rational number, but not all rational numbers have all of the attributes of a whole number.
