When you are writting a formal essay for school.
If the number is below ten, then you would use words to represent the numbers, when they are above ten, you use the number (:
they use numbers not words.
The general rule in formal writing (that which you do for school or work) is yes. All numbers that appear as two or fewer words should be written out.
Do not worry. You could use different combinations with numbers and words. First maybe pick two words you like (for example: jellyfishboom) and if it says that it was taken, then use your lucky number (for example: jellyfishboom21) you could do silly ones, serous ones, but most people use their first and last name ( maryjohns@gmail.com ) sometimes if it's taken they use numbers ( sarawhite232). see what I mean? You should try it!
Yes, numbers should be written as full words.
stylebook
Yes
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.
You can't. There is a minimal amout of words (and names) that you can use numbers to spell.
yes words are better because you use them more often
That would depend on which words you use (as they have different numbers of letters).
Any you wish