Loony Language: What To Do With Numbers

I was finishing reading a book when I hit a few sentences in a row which dealt with numbers, and I was struck by the oddity of the conventions involving spelling numbers out and using numerals.  Most of the sentences that I read involved a mix of the two.  I'll use a hypothetical example:  "One of the 2 teams will win the game."  Why not "1 of the 2 teams will win the game." or "One of the two teams will win the game."?  Either makes more sense than mixing words and numerals.  It's little wonder that students using a documentation system such as MLA or APA get confused because the conventions for numbers are a bit strange.  Some make sense such as using numerals when the numbers would be quite wordy to spell out, say 1,289,348, but most of the conventions seem purely arbitrary.  I'm pretty certain everyone understands that "1 of the 2" and "One of the two" mean the same thing however it's expressed.  I even understand "One of the 2", but it does look the goofiest.  Nevertheless, somehow conventions regarding numbers and when to spell them out have arisen when they probably aren't needed.  I suppose it gives English teachers and copy editors another way to make money, so I probably shouldn't complain, but no user of English should really have to worry about such stuff as long as everybody can understand, in this case, that only a single team will win the game.