Numeral is a word used to quantify or indicate a certain numerical or ordinal position of something or someone.
The numeral can be represented in two ways. The first one is the numeric symbol and the other is your writing in full.
What makes the numeral different from an article, for example, is that in the general context, the article indicates an indefiniteness of the noun, while the numeral indicates the quantity of the noun.
Classification of numerals
As for classification, the numeral can be:
Cardinal: when it indicates quantity or serves to account for something. Ex: One, three, five...
Ordinal: when he expresses order or sequence of something. Ex: Third, tenth, second...
Multiplicative: when it indicates multiplicative counts. Ex: Triple, double, double, sextuple...
Factional: when it expresses part of a whole or fractional portions. Ex: Third, fifth, eighth...
The numeral can also be collective when it indicates a set.
Example:"Peter bought a dozen eggs".
The use of the numeral can be in different ways. For example, in the designation of popes, kings, emperors, centuries and part of a work, the ordinal numbers up to the tenth are used. Then the cardinals are used, as long as the numeral comes after the noun.
For the designation of laws, decrees and ordinances, the ordinal numeral up to the ninth and the cardinal numeral from the tenth on is used. As for the days of the month, the cardinals are used, with the exception of the indication of the first day, which is traditionally done by the ordinal "first".
Numeral inflections
The numeral may vary depending on the quantitative indication to which it refers. In these cases, its flexion also takes place according to its classification.
Cardinal numerals are mostly invariant. However, there are two cases where they can vary: in gender (Ex: one/one, one/one, two hundred/two hundred); and in the plural of million (Ex: million/million).
Ordinal numerals can vary in gender and number. Ex: first/first/first/first
Multiplicative numerals are invariant when acting on substantive functions.
Example:"They made twice the effort and achieved triple the production".
However, when they act in adjective roles, they can vary in gender and number.
Example:"Bianca had to take triple doses of the drug".
Fractional numerals can also vary in gender and number. Ex: one-third, two-thirds, two-eighths
And collective numerals only vary in number. Ex: a dozen, two dozen, a thousand.