demi ou demie
Il est neuf heures et demie.

Il est midi et demi.

why the first one using 'demie', but the another one using 'demi' ?
Merci ~

Question

demi ou demie
Il est neuf heures et demie.

Il est midi et demi.

why the first one using 'demie', but the another one using 'demi' ?
Merci ~

Answer

Demi is invariable when it is placed before noun or adjective.
It can take the feminine mark (never plural though) when placed after.

In your case, UNE heure is feminine while UN midi is masculine.

https://www.projet-voltaire.fr/regles-orthographe/demi-ou-demie/