IX + X = XXI. So XXI is two legions into one.
Roman Numerals
Categories
Explanation
Explain Bear
Alright, listen up, buttercup. This joke is for people who couldn't count past ten with both shoes on. See, in Roman numerals, IX is 9, X is 10, and XXI is 21. The joke is about Roman legions which, BTW, is a unit of 3,000–6,000 men in the Roman army.
Anonymous
Why would 9 plus 10 be 21????