Roman numeral riddles
Every classic in one place, with the answer up front and the trick explained after. Nothing here needs more than the seven letters and one sly idea.
Which Roman numerals multiply to 35?
Answer: V and VII. V is 5, VII is 7, and 5 times 7 is 35. Since 35 is the product of two primes, that pair is the only real answer. The question is Rule 9 of The Password Game, and it has its own worked page: Roman numerals that multiply to 35, including how to make the rule actually go green in the game.
Half of twelve is seven
Answer: cut XII in half. The riddle asks you to prove that half of twelve is seven. Write twelve as the numeral XII, then draw a line through its middle and keep the top half. What remains of the letters reads VII, which is seven. The same cut turns XIII (thirteen) into VIII (eight), which is the follow-up version you will also meet: half of thirteen is eight.
The trick is a change of medium. The question sounds like arithmetic, but the answer treats the numeral as a drawing. Once you see that move, every riddle in this family opens the same way.
Take one from fifty-nine and get sixty
Answer: LIX minus the letter I is LX. Fifty-nine is LIX, where the I sits in front of the X and subtracts one from ten. Remove that I, the numeral for one, and you are left with LX, which is sixty. Taking one away made the number bigger, because what you removed was a subtraction. This is the "sixty and LIX" riddle that circulates on worksheets, and it is the neatest demonstration of the subtractive rule you will find: the same rule is explained properly in LIX meaning: 59 and LX meaning: 60.
Remove a letter from six and get nine
Answer: SIX minus the S is IX. Cross out the S in the word SIX and the remaining letters, IX, spell the Roman numeral for nine. The numeral was hiding inside the word all along. It works in the other direction too: put an S in front of IX and nine turns back into six.
The matchstick equations
Matchstick puzzles write a false Roman numeral equation in sticks and allow you exactly one move. Two classics, solved:
- X + I = IX, move one stick: take a stick out of the plus so it becomes a minus. X - I = IX is true: 10 minus 1 is 9.
- XI + I = X, move one stick: move the final I of XI across the equals sign onto the X. The equation becomes X + I = XI, which is true: 10 plus 1 is 11.
Every matchstick puzzle in this family is solved the same way: look for the stick that is doing the least work, usually in the operator or at the end of a numeral, and ask where it would turn a false statement true. The numerals themselves follow the ordinary rules, which you can check in the guide or with the converter.
The trick questions
Three questions that sound like riddles and have real answers, each with its own page:
- What is the Roman numeral for zero? There is none; the system starts at I. The full story, including what the Romans wrote instead, is at the Roman numeral for zero.
- What is the longest Roman numeral? Within the standard system it is MMMDCCCLXXXVIII, the year 3888, at fifteen letters. Why, and the runners-up, at the longest Roman numeral.
- Why do clocks show IIII instead of IV? A dialmaker's convention older than the standard rules. The history is at why 4 is IV and not IIII, and the live dial at the Roman numeral clock.
Frequently asked questions
Which two Roman numerals multiply to 35?
V and VII: 5 times 7 equals 35. They are the only non-trivial pair, because 35 is the product of the two primes 5 and 7. The question comes from Rule 9 of The Password Game.
How is half of twelve seven?
Write twelve as the Roman numeral XII, then cover its bottom half. The top half of XII reads VII, which is seven. The same cut turns XIII (13) into VIII (8).
How do you take one from fifty-nine and get sixty?
Fifty-nine is LIX. Take away the letter I, the numeral for one, and LX remains, which is sixty. The riddle works because removing the subtractive I raises the value instead of lowering it.
How can six become nine by removing a letter?
Cross out the S in the word SIX and the letters that remain, IX, are the Roman numeral for nine. It is a word trick rather than an arithmetic one: the numeral was hiding inside the word.
How do you fix X + I = IX by moving one matchstick?
Take one stick out of the plus sign, turning it into a minus. The equation becomes X - I = IX, which is true: 10 minus 1 equals 9.
Is there a Roman numeral riddle about zero?
The trick question is to ask for the Roman numeral for zero. There is none: the system starts at I, and the Romans used the word nulla when they needed to write the absence of a number.
Related
Last updated July 22, 2026. Reviewed for accuracy against the standard rules for Roman numerals. How we check accuracy.