# What are Ordinal Numbers?

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## Ordinal Numbers

What are ordinal numbers? When we are describing the order of objects we use ordinal numbers. Ordinal numbers are used to explain the position of something in a set. Ordinal numbers are used to show the order of things. This is useful in maths because it helps to keep things organised when solving maths problems or describing a maths solution.

## What are ordinal numbers used for?

Think about the word ANSWER. The letter at the start of the word is A. That means it is the number 1 letter. When something is number 1 we say it is first. The letter N comes next. If we number the letters then the letter N is number 2.

A N S W E R
1 2 3 4 5 6

When something is number 2 we say it is second. So N is the second letter in the word ANSWER. The S is number 3. When something is number 3 we say it is third. So S is the third letter in the word ANSWER. First, second and third are all ordinal numbers because they describe the order that the letters are in!

## Ordinal Numbers – Spelling Rules

To make most ordinal numbers after 3 you just need to add a -th to the end or -ieth if the number ends in a -y. For example, if you start with four and a -th you now have fourth which is the ordinal form of four. If you start with twenty, remove the -y and add -ieth you now have twentieth. This method works for most ordinal numbers but there are exceptions. The -v in the numbers five and twelve become -f in their ordinal form so five becomes fifth and twelve becomes twelfth.

These are the ordinal numbers from 1 to 12.

cardinal number ordinal number short form
one first 1st
two second 2nd
three third 3rd
four fourth 4th
five fifth 5th
six sixth 6th
seven seventh 7th
eight eighth 8th
nine ninth 9th
ten tenth 10th
eleven eleventh 11th
twelve twelfth 12th

Let’s look at the ordinal numbers in multiples of 10.

cardinal number ordinal number short form
ten tenth 10th
twenty twentieth 20th
thirty thirtieth 30th
forty fortieth 40th
fifty fiftieth 50th
sixty sixtieth 60th
seventy seventieth 70th
eighty eightieth 80th
ninety ninetieth 90th
hundred hundredth 100th

Hyphenated numbers keep the first word then use the ordinal version of the second number. Here are some examples of hyphenated ordinal numbers.

cardinal number ordinal number short form
thirty-six thirty-sixth 36th
seventy-seven seventy-seventh 77th
twenty-one twenty-first 21st
forty-three forty-third 43rd
fifty-four fifty-fourth 54th

## Ordinal Numbers – Example

Look at the picture below. What is the ordinal number for the kid in the green shirt?

Remember:

• The first step is to find the kid in the green shirt.
• The second step is to find the front of the line. We can tell the start of the line is on the left because all of the students are facing left.
• The third step is to count from the front of the line to the kid in the green shirt.
• The fourth step is to identify that number as the answer.

The kid in the green shirt is fourth in line.

## Ordinal Numbers – Summary

Ordinal numbers helped solve the problem and they helped to explain how to get to the answer. Ordinal numbers can be really useful! If you want to determine a position of someone or something within a group, you can use ordinal numbers to describe the order of a set. Let’s have a look at the steps to take in order to determine someone’s or something’s position in a group.

Step # What to do
1 Find the person or object in a group to
which you want to assign an ordinal number to.
2 Find the front or back of the line.
3 Count from the front or the back to
4 Identify the number matching the
person’s or object’s position.
5 Change the number to the number’s ordinal
form by either adding -th or using one of the special forms.

You can use our interactive exercises and worksheets to practice using ordinal numbers.

## Frequently Asked Questions Concerning Ordinal Numbers

What are the Ordinal Numbers?
What are ordinal numbers used for in maths?

## What are Ordinal Numbers? exercise

Would you like to apply the knowledge you’ve learnt? You can review and practice it with the tasks for the video What are Ordinal Numbers?.
• ### What are ordinal numbers?

Hints

The word ordinal gives you a clue to the purpose of ordinal numbers. What does the word ordinal sound like?

Ordinal numbers can be both even and odd.

First, second and third are all examples of ordinal numbers.

Solution

Ordinal numbers show the order or position of a number! First, second and third are all examples of ordinal numbers.

• ### Pair the ordinal and non-ordinal numbers.

Hints

Remember, ordinal numbers are often just the cardinal number with a "-th" at the end of the number!

The ordinal numbers for one, two and three don't follow the "-th" ending rule.

Solution

Here are the matching numbers!

one: first

three: third

four: fourth

six: sixth

seven: seventh

ten: tenth

• ### Match the ordinal numbers.

Hints

Remember, some ordinal numbers are different and don't put a "-th" at the end of the number.

One, two and three don't place a "-th" at the end of the number to become ordinal numbers.

Solution

Here are the correct ordinal number pairs from this activity!

1st: first

2nd: second

3rd: third

4th: fourth

5th: fifth

The other ordinal numbers are incorrect. These added a "-th" to the end of each number, but these numbers are different and don't follow that rule.

• ### What are the ordinal numbers?

Hints

Hyphenated regular numbers keep the first word the same and the "-th"gets added to the last word.

Adding a "-th" to the end of most numbers makes them ordinal numbers.

Solution

All of these numbers use the normal "-th" rule to become ordinal numbers. Here are the correct numbers!

21: twenty-first

18: eighteenth

26: twenty-sixth

33: thirty-third

10: tenth

• ### Which are the ordinal numbers?

Hints

Remember, ordinal numbers are often just the cardinal number with a "-th" at the end of the number

Second is the ordinal version of two.

Solution

Second, fourth, seventh, ninth, eleventh, fifteenth and seventeenth are all the ordinal numbers from this activity!

• ### What are the ordinal numbers?

Hints

Remember, numbers that normally end in a "y" will have an "-ieth" ending as an ordinal number.

Hyphenated regular numbers keep the first word the same and the "-th"gets added to the last word

Look at these examples of ordinal numbers being written out.

7: seventh

15: fifteenth

Solution

All of these numbers didn't follow the "-th" rule in some way. Here are the correct ordinal numbers.

1: first

2: second

3: third

5: fifth

13: thirteenth

30: thirtieth

52: fifty-second