Basic 4 · Mathematics · Counting, Representation and Cardinality

Roman Numerals up to 30

In this topic you will read and write Roman numerals from 1 to 30.

By the end of these notes you should be able to:

Name the Roman symbols I, V and X
Use the rules for writing Roman numerals
Change between Roman and Hindu-Arabic numerals up to 30

What you already know

Place value

Copy everything that has a blue line on its left into your notebook. The other parts are for reading.

Strand: Number
Sub-strand: Counting, Representation and Cardinality
Indicator: B4.1.1.1.6 – Develop an understanding of the Roman numeral system up to XXX (30)

Introduction

Look at some clocks and at chapter numbers in books. You may see I, V and X instead of 1, 5 and 10. These are Roman numerals, used by the ancient Romans.

1. The Symbols

Roman symbols

Roman	Value
I	1
V	5
X	10

2. The Rules

Add when a symbol is followed by an equal or smaller one: VI = 5 + 1 = 6; XX = 10 + 10 = 20.
Subtract when a smaller symbol comes before a larger one: IV = 5 − 1 = 4; IX = 10 − 1 = 9.
Do not repeat a symbol more than three times: 4 is IV, not IIII.
V is never repeated.

3. Numbers 1 to 30

Roman numerals 1–30

1 I	2 II	3 III	4 IV	5 V
6 VI	7 VII	8 VIII	9 IX	10 X
11 XI	12 XII	13 XIII	14 XIV	15 XV
16 XVI	17 XVII	18 XVIII	19 XIX	20 XX
21 XXI	22 XXII	23 XXIII	24 XXIV	25 XXV
26 XXVI	27 XXVII	28 XXVIII	29 XXIX	30 XXX

A clock face with Roman numerals I to XII — Figure 1: A Roman numeral clock Draw a clock with Roman numerals.Illustration: Sirbus

Example

Write 24 in Roman numerals.

24 = 20 + 4
20 = XX
4 = IV

Answer: XXIV

Example

Write XIX as a number.

X = 10
IX = 9

Answer: 19

New words

Roman numerals: Number symbols used by the ancient Romans.
Hindu-Arabic numerals: The digits 0–9 we use every day.
symbol: A sign that stands for something.
subtract: To take away.
repeat: To use again.
ancient: Very old.

Summary

I = 1, V = 5, X = 10.
Add when a smaller or equal symbol follows; subtract when a smaller one comes first.
A symbol is never repeated more than three times.
Example: 24 = XXIV and 19 = XIX.

Class activity: Roman Match

Make cards with numbers 1–30 and their Roman numerals.
Mix them and match each pair.
Write your age and the date in Roman numerals.

You need: Bundles of sticks, Locally made Roman numeral cards, Exercise books

Exercises

Answer in your exercise book first, then check your answers.

1. What is VII?
- A. 7
- B. 6
- C. 8
- D. 12
Show answer
Answer: 75 + 1 + 1 = 7.
2. Which is 14 in Roman numerals?
- A. XIV
- B. XIIII
- C. IVX
- D. XVI
Show answer
Answer: XIV10 + (5 − 1) = 14.
3. What is XXIX?
- A. 29
- B. 31
- C. 21
- D. 19
Show answer
Answer: 2920 + 9 = 29.
4. X stands for 10.
- A. True
- B. False
Show answer
Answer: TrueX = 10.
5. IIII is the correct way to write 4.
- A. True
- B. False
Show answer
Answer: False4 is IV.
6. 30 in Roman numerals is ______.
Show answer
Answer: XXX10 + 10 + 10.
7. Write 18 and 26 in Roman numerals.
Show answer
Answer: XVIII and XXVI10 + 8 and 20 + 6.
8. Why is 9 written as IX and not VIIII?
Show answer
Answer: A symbol cannot be repeated more than three times, so we subtract: 10 − 1.That is the Roman rule.

Homework

Find Roman numerals on a clock, watch or book. Write what number each one stands for.