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Roman numerals

Reading and writing the symbols up to M (1000).

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Long ago, the Romans wrote numbers with letters. You still see Roman numerals today: on clocks, in book chapters and at the end of film credits.

In this lesson you will learn:

  • the seven symbols and what each one is worth
  • the two rules: when to add and when to take away
  • how to write any number up to 1000 in Roman numerals
  • how to read Roman numerals back as ordinary numbers

1. The seven symbols

Key idea Roman numerals use just seven symbols. Every number is made by putting them together.
IVXLCDM
1510501005001,000
A way to remember I Value Xylophones Like Cows Do Milk. The first letters are the symbols in order, from smallest to biggest.
  • The symbols go 1, 5, 10, 50, 100, 500, 1000. Each one is either 5 times or 2 times the one before.
  • The Romans had no symbol for zero.

2. The two rules: add or take away

Rule 1: add When the symbols go from biggest to smallest, add them up. VI = 5 + 1 = 6. XVII = 10 + 5 + 1 + 1 = 17.
  • I, X, C and M can be used up to three times in a row: III = 3, XXX = 30, CCC = 300.
  • V, L and D are never used twice in a row. VV would just be X.
Rule 2: take away When a smaller symbol comes before a bigger one, take it away. IV = 5 − 1 = 4. IX = 10 − 1 = 9.

Only these six pairs take away. Learn them:

IVIXXLXCCDCM
494090400900
Watch out 4 is IV, not IIII. And you can only take away I, X or C, from the next two symbols up. So 99 is not IC.

3. Writing a number in Roman numerals

Key idea Split the number into hundreds, tens and ones. Write each part in Roman numerals, then join them up in that order.

The same pattern repeats in every column. Only the symbols change:

DigitOnesTensHundreds
1IXC
2IIXXCC
3IIIXXXCCC
4IVXLCD
5VLD
6VILXDC
7VIILXXDCC
8VIIILXXXDCCC
9IXXCCM

Example: write 594 in Roman numerals

  • Split it: 594 = 500 + 90 + 4.
  • Write each part: 500 = D, 90 = XC, 4 = IV.
  • Join them up: D + XC + IV = DXCIV.
AnswerDXCIV
Watch out Always split first. 99 = 90 + 9 = XC + IX = XCIX. A shortcut like IC is wrong.

4. Reading Roman numerals

Key idea Read from the left. Look out for a smaller symbol in front of a bigger one: that pair is one of the six take-away pairs.

Example: what number is CDXLVII?

  • CD is a pair: 500 − 100 = 400.
  • XL is a pair: 50 − 10 = 40.
  • VII = 5 + 1 + 1 = 7.
  • 400 + 40 + 7 = 447.
Answer447

The mistakes that cost marks

  1. Using four of the same symbol. 4 is not IIII and 40 is not XXXX. use a take-away pair: IV = 4, XL = 40.
  2. Making up a take-away pair. 99 is not IC and 49 is not IL. split first: 99 = 90 + 9 = XCIX, and 49 = 40 + 9 = XLIX.
  3. Adding a pair instead of taking away. XL is not 60. the smaller symbol is in front, so take away: 50 − 10 = 40.
  4. Repeating V, L or D. VV is not how the Romans wrote 10. use the symbol for that number: X.
  5. Mixing up D and M, or L and C. say the rhyme: I Value Xylophones Like Cows Do Milk. L = 50, C = 100, D = 500, M = 1000.

Quick checklist

Tick each one when you can do it without help.

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