Numbers and math

A classic question is: how do you count to ten in your conlang?
Generalizing:
 - do you form ordinals from cardinals? how? if not, how?
 - do you have a zero?
 - can numbers be negative?
 - fractions? percentiles? if it's not a decimal system, is there
   something instead of percentiles?
 - how do you add, subtract, multiply and divide? (if you know how)
 - what about raising to the nth power and n-roots?

I think I'll stop there but you get the idea :)

I'm asking because there are lotsa new langs here, plus I've finally
gotten those much wanted târuven numbers from 0 to 10 in place, but my
guesses at how higher numbers (for instance 73 (decimal)) are formed
somehow feels wrong, so I need tips (actually I need a târuven book on
mathematics but I haven't found any so far ;) ).


t.