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Roman Numerals 1-20

Roman Numerals 1-20
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  • 0:01 Numbers
  • 0:43 Roman Numerals Basics
  • 1:42 Roman Numerals Rules
  • 3:40 Roman Numerals 1-20
  • 5:27 Lesson Summary
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Lesson Transcript
Instructor: Yuanxin (Amy) Yang Alcocer

Amy has a master's degree in secondary education and has taught math at a public charter high school.

After watching this video lesson, you will be able to identify and write the numbers 1-20 using Roman numerals. You will learn how a Roman numeral is different from the numbers we are familiar with, and you will learn the rules of Roman numerals.

Numbers

In this video lesson, we're going to explore a different way of writing our numbers. Right now, you are familiar with the Arabic numerals, the ten digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. These are the numbers you see day in and day out. You go to the store and you see these numbers written all over the place to let you know how much things cost. Out on the road, these same Arabic numerals are posted on signs everywhere, telling you how fast you can drive. We are so used to writing down our numbers using Arabic numerals that we don't even think twice about writing down a phone number using these numerals when our friend tells us his phone number.

Roman Numerals Basics

But did you know that there is another way you can write down numbers? This other way was used by the Romans well over 2,000 years ago. These numbers are referred to as Roman numerals. Instead of the ten digits that we are familiar with, we have just seven symbols: I, V, X, L, C, D, and M. Each of these symbols represents a different amount. Here's a table showing you what each letter represents.

Symbol Value
I 1
V 5
X 10
L 50
C 100
D 500
M 1,000

When you write Roman numerals, all your letters are upper case. You write your Roman numeral from left to right, just like you would write your regular numbers, but Roman numerals do follow a few interesting rules.

Roman Numerals Rules

Roman numerals are written by combining the various symbols and adding or subtracting their values. Just like when writing with our usual Arabic numerals, Roman numerals are written with the larger number values first. For example, to write five hundred seventy-three, we write 573 and not 357. We first use the 5 because we have five hundreds, then we enter 7 because we have seven tens, and then finally, 3. It is the same for Roman numerals. We write the larger values first.

As you can see, we only have seven Roman symbols to pick from. So in order to write out our numbers, we sometimes need to write the same symbol more than once so we can add them up to the number that we want. For example, to write 1, we write I. But what if we wanted to write 3? We would write the I three times in a row: III.

There is one rule that makes writing Roman numerals interesting. This rule tells us that we do not want to write the same symbol four times in a row. To avoid doing this, we write a smaller symbol in front of a larger symbol. This tells us to subtract the smaller number from the larger. For example, to write the number 4, we don't write IIII. Instead, we write IV. We have a smaller symbol, the I that stands for a 1, in front of the V that stands for a 5. This tells us to subtract the 1 from the 5. What do we get? 4.

All of the symbols follow this rule. For example, IX gives us 9 and XC gives us 90. This is the only time when we subtract. We add at all other times. So XX gives us 20, since we are adding.

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