🏛️ Topics & explainers · 5 min read
Roman numerals for Class 4: the seven letters and the subtraction rule
A Class 4 explainer of Roman numerals — the seven symbols, when to subtract, worked examples, and the illegal-numeral trap in SOF IMO papers.
Roman numerals are an older way of writing numbers using seven letters: I (1), V (5), X (10), L (50), C (100), D (500) and M (1000). Class 4 children mostly work with numbers up to 100. The whole topic comes down to one reading rule — and olympiad questions test whether a child applies it carefully.
The idea in one minute
- When a smaller symbol comes after a bigger one, add: VI = 5 + 1 = 6.
- When a smaller symbol comes before a bigger one, subtract: IV = 5 − 1 = 4.
- Only I, X and C are ever subtracted, and only from the next two bigger symbols: IV, IX, XL, XC.
- A symbol never repeats more than three times: 40 is XL, never XXXX.
✏️ Warm-up: read a numeral
What number does XIV stand for?
- A14
- B16
- C4
- D24
Show the answerAnswer: 14
Answer: 14. Read left to right: X is 10, then IV — the I comes before the V, so subtract: 5 − 1 = 4. Together, 10 + 4 = 14. A child who adds every symbol (10 + 1 + 5) gets the trap answer 16.
✏️ Level up: write 49 correctly
Which is the correct Roman numeral for 49?
- AXLIX
- BIL
- CXXXXIX
- DXLVIIII
Show the answerAnswer: XLIX
Answer: XLIX. Break 49 into 40 + 9. Forty is XL (50 − 10) and nine is IX (10 − 1), so 49 is XLIX. IL is illegal because I may only be subtracted from V or X, not L. XXXXIX repeats X four times, and XLVIIII repeats I four times — both break the three-repeat rule.
✏️ Olympiad twist: arithmetic with numerals
What is XC − XL, written as a Roman numeral?
- AL
- BLX
- CXL
- DC
Show the answerAnswer: L
Answer: L. Convert first, calculate, then convert back. XC is 100 − 10 = 90 and XL is 50 − 10 = 40. Then 90 − 40 = 50, which is the single symbol L. Doing the arithmetic on the letters themselves is where children slip — always go through ordinary numbers.
Roman numerals form a short, satisfying run of levels in LittleMathematicians’s Class 4 Number Sense topic — reading first, then writing, then spot-the-illegal-numeral questions as mastery grows. It is free during early access, so it is an easy topic to let your child try first.
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