What are all the possible combinations that add up to 2.25?

There is an infinite number of combinations.

They can be expressed as x + y = 2.25 . If you choose onenumber as x you can calculate the y to give the correct result using the equation y = 2.25 - x .

e.g. x = 1, y = 1.25 etc.

You can substitute any number for x.