I don't make the rules. XP
Apparently there has been some big debate as to whether or not math is a science, for at least a couple hundred years.
People in favor of considering mathematics a science say that it goes back to the root meaning of "science" as a "field of knowledge". Even in the contemporary sense of the term "science", they argue that there are still instances where you would use experimentation to prove or disprove a hypothesis. Naturally though that only happens if you are developing some new formula or something like that.
I guess it kind of makes scene. It is just that we have established so much of mathematics already that it doesn't seem like science because there isn't as much experimental stuff going on with it directly.
There is one thing that invalidates maths that are applied to it, blackholes! XD
Personally, I don't really see the justification for math being a science either, but I just kind of go with it.