We use numbers to count and indicate how many nouns are being described. The main challenges in writing numbers involve the forms and spelling.
Let's first consider the words Spanish uses for cardinal numbers:
Ordinal numbers allow us to establish an order or rank, e.g.: "first", "second", "third" (primero/a/primer, segundo/a, tercero/a/tercer). The main ordinals in Spanish are presented in the following table:
Ordinal numbers can also appear in the plural to match the number of the noun they modify, e.g.: Ellas eran las quintas en llegar.
Ordinal numbers also usually go in front of the noun they modify, e.g.: Es el tercer presidente del club. When the forms primero and tercero appear directly in front of a masculine noun they drop their final "o" as seen in the previous example.
It is common in Spanish to abbreviate ordinal numbers. To abbreviate ordinals, use a decimal after the number and then superscript letters depending on which ordinal you are using. Use "er" for primer and tercer only, e.g.:
Use a superscript degree sign º for masculine ordinal numbers and a superscript letter ª for feminine ordinal numbers, e.g.: