Some people have poor handwriting which may not be easy to read. Writing the amount in two ways allows for verification.
The use of words as well as numerals presumably makes it harder to alter a check.
It is still a number.
Written form means you have to write your answer in words, not numerals: ten, not 10.
1942 IS written in Arabic numerals. MCMXLII is the same number written in Roman numerals.
5 in Roman numerals is written as: V
In numerals : 1,150,000,000,000 In words: one trillion, one hundred fifty billion
4000 is written in Roman numerals as MMMM.
1900 is written in Roman numerals as MCM.
In Roman numerals the number 77 is written as LXXVII.
The legal amount of a check is the amount written out in words. The amount on the check in numbers is the courtesy amount.
The number 2100 is written as MMCI in Roman numerals.
Seven tens or 70 is written LXX in Roman numerals.