According to the MLA Handbook for Writers of Research Papers (Seventh edition), for most MLA style papers, spell out numbers written in one or two words such as "two" or "three hundred." If you begin a sentence with a number, spell it out, even if it is a date or other number that uses more than two words. When using large numbers, as long as they do not start the sentence, you can use a combination of numerals and words, such as "3.6 billion." Write out spans of time such as "sixteenth century."
Use numerals for large numbers that do not allow for a smooth combination of numbers and words, such as "151." In papers that rely heavily on numbers, focusing on mathematical or scientific concepts or containing many statistics, use numerals before measurement terms, such as "3 centimeters" and data comparisons such as "the scores rose from 7 to 12." Use numbers to represent amounts of money, in addresses, with symbols such as "%" and "lb.," in decimal representations and for specific dates.
Use the same structure for all portions of ideas that demonstrate a comparative relationship, such as "4 of the 310 members." Use commas between every three digits from the right in large numerals ("1,000" and "352,000,000"). Type symbols such as "$" for money amounts and percentages in MLA. Use consistent order for information in dates: day-month-year with no punctuation (12 January 1990) or day-month-year with a comma after the day and another after the year unless the date appears at the end of a sentence (January 12, 1990).