How to make numbers like 4,6 to 0,6 and 5,3 to 0,3 with a mathematical formula using only "classic" math?

The only number I got to do math with is 4,6

Nothing more

I can't choose which part of the number or anything like that, so I'm looking for a formula which does something like that

Thank you, but modulo does not include in the "clasic" math I was thinking about, more along the lines of * / + 1 ^ 

I could do modulo manually if I had a method of flooring the number, but then I could just do it directly anyways :/

 

Thanks thought