You use this to say what the position (rang) is of something
Example
first place
May seventh
Rule to follow: Cardinal numbers (hoofdtelwoorden) are about the position (rang).
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Similair to cardinal numbers 11 (eleven) until 19 (nineteen) are irregular (they don't make sense), so learn them by heart! (leer het uit je hoofd)
20- twentieth 70- seventieth
30- thirtieth 80- eightieth
40- fortieth 90- ninetieth
50- fiftieth 100- hundredth
60- sixtieth
1. Begin with the first number--> thirty
2. add a dash (streepje) --> thirty -
3. Add the second number --> thirty - fourth