"The two boys sleep."

Translation: Duo pueri dormiunt.

[Athalawulfaz]

Why 'duo'? Shouldn't the number match the inflections of the noun for unus/a/um, duus/a/um and trius/a/um?

This should be 'dui pueri dormiunt'.

[Profe112]

"Duo" is masculine and neuter plural. "Duae" is feminine plural.

[Danielconcasco]

No, that's not how duo declines. Duo is the nominative.

[suhridmulay]

Is there some resource for learning all word endings in Latin?

[AllemandeLeft]

I don't now if your post is current, but
here's the address of a website http://www.latein-online.net/index.php?section=deklinationao.htm . It's in German, but I think in this case it is equal.

[CoralLorna]

Why does duo go in front of boys (pueri) but behind the noun men or (vir )
Where does the number normally go and why does it move around in the sentence please ?

[Krzywe_Kolano]

The word order is flexible in Latin to some extent, since the declension makes the role of each word obvious (usually).