 Hong Kong
Stage 1 - Stage 3

# Roman Numerals

Lesson

We can thank the Romans for for a lot of cool stuff we have today like plumbing, sanitation and public baths and swimming pools for example.

Roman numerals are a different way of writing numbers, and they were used in places around the world before we had the Arabic numbers we use today. We study them mostly because it's cool to recognise them in places when they are used, and to appreciate the historical context that surrounds other number systems.

I in Roman Numerals means a count of $1$1. So II is $2$2, III is $3$3, and so on.

You can imagine how boring it would be to then have to write $8$8, IIIIIIII or even $108$108

So when they get to $5$5, they group them together and call them V.

This makes VI to be $5+1=6$5+1=6 and VII is $5+1+1=7$5+1+1=7

For ten use X, C for hundred (from the Latin Cent - meaning 100).  50 is L

Remember!

I - 1
V - 5
X - 10
L - 50
C - 100
D - 500
M - Thousand

So far so good.  The Romans thought that would be quicker to write $10$10 less than $50$50, for $40$40 than to write $10+10+10+10$10+10+10+10.

So for $40$40 in Roman Numerals would be XL ($10$10 before $50$50), similarly for $4$4 - IV - $1$1 before $5$5.

## Try these on for size.

XLIV - 10 before 50 and 1 before 5 => $40+4=44$40+4=44 Two digit Roman Numerals

LXVII - 50 and 10 and 5 and 1 and 1.... $67$67 Two digit Roman Numerals

DCCCXC - 500 and 100 and 100 and 100 and 10 before hundred becomes $800+90=890$800+90=890 Three digit Roman Numerals

Writing numbers in roman numerals can be done as well

$2383$2383 $=$= MM (2 thousand) CCC (3 hundred) LXXX (eighty) and III (three) - MMCCCLXXXIII

$999$999 $=$= CM (100 before a thousand - 900) XC (ten before the hundred - 90) and IX (one before the ten - 9) - CMXCIX

$756$756 = DCC (500 + 200) L (50) and XI (6) DCCLXI

An amazing fact about Roman Numerals is that they do not have a symbol for zero, if you have no tens, you don't write any tens down.

#### Worked Examples

##### Question 1

These three examples show how to convert from Roman Numerals into regular numbers.

##### Question 2

These examples show how to convert from normal numerals into Roman numerals.

Want to see more like this problem?
Try these:

##### Question 3

These examples show how convert from Roman numerals when the symbols are not in decreasing order.

Want to see more like the ones above?

Try these: