For non financial or statistical writing, that is for text, it is most common to spell out numbers under thirteen (13).
in algebra
If the number is below ten, then you would use words to represent the numbers, when they are above ten, you use the number (:
That would depend on which words you use (as they have different numbers of letters).
Please use words for the math functions, such as "divided by" or "squared" or whatever functions you would need to use with the numbers.
You would use lower for degrees. :)
stylebook
You would use lowest common multiple in fractions if you have to use pictures, numbers and words. (Sometimes, depending on the teacher, you might get higher marks if you put the fraction into its smallest form!)
I would hope all elections use rational numbers: all Counting numbers are Rational numbers.
Variables.
When working with very large numbers or very small numbers and they would use a system of numeracy known as scientific notation.
When you are writting a formal essay for school.
Your question does not state what to DO with the numbers, so it cannot be answered. You need to use words like "divided by" or "plus" or "times" or some kind of words telling what mathematical function to use with the numbers.
yes words are better because you use them more often