Ordinal numbers are those that express a position of an element or a set of elements in an ordered sequence. In contrast to the cardinal numbers that represent quantity, ordinal numbers incorporate an order, and are accompanied by a noun.

In short, ordinal numbers are used to express in words the position that an element occupies within an ordered series, and these have as their main function to count and order elements or sets of elements.

Function of ordinal numbers

Ordinal numbers are used to:

  • Put things in sequence. Example: Spain came first in the soccer playoffs.
  • Give the date only of the 1st of each month. Example: Marta’s birthday is the first of March.
  • Name the floors of a building. Example: Luis’s apartment is on the eighth floor.
  • Indicate the numbers of the festivals or versions , whether of books, films, software, etc. Example: This is the seventieth festival of the Viña del Mar song.
  • They give each element of a set a place. Example: by listing kitchen appliances such as plates, silverware, glasses, and pans; where dishes are listed first , while pans are fourth

Gender in ordinal numbers

Ordinal numbers are adjectives and must match the noun they refer to in gender and number. If the ordinal number refers to a feminine noun, an “a” is placed at the end, while if the reference is to a masculine noun, a letter “o” is written at the end. If the nouns are plural they end with the letter “s” at the end.

Example of male and female ordinal numbers in:

Feminine Masculine Plural

1st First 1st first 1 as  First – 1 os   First

2nd Second 2nd Second 2 the Second – 2 the Seconds

3rd Third 3rd Third 3 as Third – 3 years Third

Ordinal number abbreviations

There are some rules to abbreviate ordinal numbers of which the following stand out:

  • The point must always be written in the abbreviations in the ordinal numbers , placing it between the figure and the flown letter, otherwise its writing will be confused with the degrees (360º), since both elements have similarity. Example: when writing eighth it should be put like this º , or sixth, like this 6.º.
  • The flown letters can be underlined or not according to your preference.
  • There must always be a correspondence between the abbreviation and the flown letter, in the content of the abbreviated expression.
  • Most of the flown letters are a (ª) or o (º), although there are cases, such as the apheresis of the first place or first place and that of the third or third place, where the last two letters are written 1. er 3. er , 31. er , 33.
  • To write the flown letters in the plural, the ª or the º should not be used, instead the apocopated forms as and os , respectively, are used.
  • If for some reason it is not possible to write the flown letters, they can be used as an abbreviation to the Roman numerals . Example: you can write VI for ninth. However, this abbreviation has a limited use of cases, such as centuries, titles, dynasties, among others.
  • It is not functional to write the abbreviations of ordinal numbers wrong. Example: it is incorrect to write 10th floor, it should be 10th floor. To name an anniversary it is wrong to write “anniversary number eight”, it should be “eighth anniversary” or “8th anniversary”.

Types of ordinal numbers

There are two types of ordinal numbers which are:

1. Simple ordinal numbers.

They are the ones that have their own shape. The simple ordinals correspond to the numbers from 1 to 10 (first, second, third …); those that correspond to the numbers from 20 to 90 (twentieth, thirtieth, fortieth …); those corresponding to the numbers from 100 to 900 (one hundred, two hundred, three hundred, …); and there are all the other numbers that correspond to the units of a thousand, which are created by adding a cardinal number giving it the ending th : thousandth, millionth, billionth, etc.

2. Compound ordinal numbers.

They are all the numbers formed by the sum of simple ordinals. To form a compound ordinal, you just have to join simple ordinals. The numbers corresponding to the tens and hundreds are created by delaying the higher order ordinal to the corresponding lower ordinals (fourteenth, twenty-fifth, thirty-third, two-hundred-first, …)

The compound ordinals corresponding to the thousands, millions and higher numbers, are formed by determining the cardinal number that multiplies it to the simple ordinal and they are postponed to the ordinals corresponding to the lower order (two thousandth, six hundred thousandth, one billionth …)

How to write compound ordinal numbers?

To form compound ordinals, simply write the ordinal corresponding to each digit from left to right. If the numeral is feminine, each word is expressed separately in feminine. The same goes for plural forms. Numerals between 13th and 29th can also be written as two separate words: thirteenth and twenty-ninth.

Some examples of this are:

  • º: It is written in masculine, two thousand three hundred forty-fifth.
  • ª: It is written in feminine, two thousand three hundred forty-fifth.
  • as Olympiads: In case of using plural it would be, the 31. as  (thirtieth first) Olympics.

Alternative ways to write ordinal numbers

Some ordinal numbers have the peculiarity of having alternative forms, and although they are less frequent, they are also considered correct when said or written. Example:

Ordinal Normal Writing Alternative Writing

3rd Third Third

7.º Seventh Seventh

9.º Ninth Ninth

11th Eleventh Eleventh

12th Twelfth Twelfth

13 th thirteenth Thirteenth

18th 18th 18th

19.º Nineteenth Nineteenth

A common mistake is to use fractional numerals as if they were ordinals. As frequent as it is, it is not considered acceptable. Example: write the fourteenth floor instead of the fourteenth floor .

There is also the word nth, which is used to express some indeterminate large ordinal. Example: For the umpteenth time, don’t do that!

Examples of ordinal numbers.

To get an idea of ​​how ordinal numbers can be used, we cite some examples:

  • Luisa is about to start a trip to the beach with her husband and children, therefore she must pack everyone’s bags. In order not to forget what to bring, she plans a special place for each item, so she decides to pack the towels first, put the swimsuits second , include the sunscreen in the third place, and reserve the fourth place for the bathing suits. your children’s beach toys.
  • Let’s look at another example: In an emergency situation, such as a fire, rescuers establish priorities to evacuate survivors. They are first in charge of saving the elderly and children, secondly they are in charge of saving pregnant women, thirdly they help all other women and fourth and last they save men.
  • Children can be taught ordinal numbers through fun games to play in the classroom, including: teaching them to count and order animals, plants, insects, and objects from nature, which can be ordered by specifying its importance by specifying the first , second , third , etc. You can also design cards with the ordinal numbers written on them and make the students games where they have to say the name of the ordinal number that they play, until they discover all the cards.

List ordinal numbers from 1 to 100

1 first 21 twenty-first 31 thirty-first 41 forty-first
2 second 22 twenty-second 32 thirty-second 42 forty-second
3 third 23 twenty-third 33 thirty-third 43 forty-third
4 fourth 24 twenty-fourth 34 thirty-fourth 44 forty-fourth
5 fifth 25 twenty-fifth 35 thirty-fifth 45 forty-fifth
6 sixth 26 twenty-sixth 36 thirty-sixth 46 forty-sixth
7 seventh 27 twenty-seventh 37 thirty-seventh 47 forty-seventh
8 eighth 28 twenty-eighth 38 thirty-eighth 48 forty-eighth
9 ninth 29 twenty-ninth 39 thirty-ninth 49 forty-ninth
10 tenth 30 thirty-40 forty-50 fifty-fifty

51 fifty-first 61 sixty-first 71 seventy first
52 seconds fifty 62 seconds sixtieth 72 seconds seventieth
53 fifty-third 63 third sixtieth 73 third seventieth
54 fifty – fourth 64 sixtieth 74 seventy-fourth
55 65 75 seventy-fifth fifth sixty – fifth fifty
66 sixty 56 sixth fiftieth sixth 76 seventy-sixth
57 fifty-seventh 67 sixty-seventh 77 seventy-seventh
58 fifty-eighth 68 sixty-eighth 78 seventy-eighth
59 fifty-ninth 69 sixty-ninth 79 seventy-ninth
60 sixty-70 seventy-eighty 80 eighty

81 eighty first 91 ninety first
82 seconds eightieth 92 seconds ninetieth
83 eighty-third 93 third ninetieth
84 eighty fourth 94 ninety fourth
85 eighty-fifth 95 fifth ninetieth
86 eighty-sixth 96 sixth ninetieth
87 eighty-seventh 97 seventh ninetieth
88 eighth eightieth 98 eighth ninetieth
89 eightieth ninth 99 ninety-ninth
90 ninety 100 hundredth

Ordinal numbers greater than 100

Ordinal numbers greater than 100 are not used as frequently, as those from 1 to 100. They are always used separately and in correspondence with gender.

     Ordinary Number M and F Male Writing Female Writing

100th – 100th Hundredth Hundredth

200.º – 200.ª Two hundred and two hundredth

300.º – 300.ª Tricentésimo Tricentésima

400th – 400th Forty-hundredth Forty-hundredth

500.º – 500.ª Five hundredth

600.º – 600.ª

700th – 700th Septing hundredth Septing hundredth

800.º – 800.ª

900.º – 900.ª Noningentésimo Noningentésimo

1000th – 1000th Thousandth

Conclusion on ordinal numbers

We can conclude that ordinal numbers represent a fundamental pillar in mathematics, because they are the only way to express the numbers to which a sequential order is placed. They have also become part of speech, unconsciously or consciously applying ordinal numbers.

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Dr. Samantha Robson ( CRN: 0510146-5) is a nutritionist and website content reviewer related to her area of ​​expertise. With a postgraduate degree in Nutrition from The University of Arizona, she is a specialist in Sports Nutrition from Oxford University and is also a member of the International Society of Sports Nutrition.

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