When to write out numerals...

Question

I was always told to write it out if the number was two digits or less ( for example "I have ten pens" not " I have 10 pens") althogh some may have been taught diffrently. Is it the same in Spanish? If not, then what is the rule?

Answer 1

This doesn't answer your entire question, but I can tell you that centuries are written like this: el siglo XX (rather than "the twentieth century"/the 20th century" as we write in English). This is pronounced el siglo veinte.