Salvete omnes. I need someone to please check me on this to see if I am correct and to correct me if I am wrong. I want to say “The month of January has 31 days”. Simple Latin,I know,should be a no-brainer but I have to be sure that what I am saying is 100% correct.
My way: " Mensis Ianvarii triginta vnvs dies habet."
My reasoning behind this:
mensis-nominative singular (month)
Ianvarii-genitive singular (OF Ianvarivs)
dies-accusative plural,object of the verb “habet”
Now for the number XXXI. This is where I am really stumped. Should XXXI also be in the accusative case or is it correct as it is?
Thanks you in advance to anyone who can help me out with this one.
I think that here may be used the dative of posession: mensi ianuario unus et triginta dies sunt.
Now for the number XXXI. This is where I am really stumped. Should XXXI also be in the accusative case or is it correct as it is?
Cardinal numbers from 4 to 100 are indeclinables. So you have to decline just unus.
I have to be sure that what I am saying is 100% correct.
Then it’s better that you wait that someone else confirm this, because I am not any guarantee 
Thank you,Hulien for your response.
Sic est: “Hoc mensis triginta unum [accusativo casu quod accusativo dies ] dies habet” seu “Hoc mensis unum et triginta dies habet”
Vide hoc exemplum: http://books.google.co.uk/books?id=5fMvAAAAYAAJ&pg=PA68&lpg=PA68&dq="triginta+unum+dies"&source=bl&ots=OtOL3XAFnW&sig=UXyunesYaT0orVCcRoan3ZQj3-Q&hl=en&sa=X&ei=D_hxU87wDc-M7AbwzoGYAg&redir_esc=y#v=onepage&q="triginta%20unum%20dies"&f=false
et hoc: “Annus et Menses”, Lingua Latina Per Se Illustrata, Familia Romana.
Et nota hoc: “Martius unum et triginta dies longus est”. Accusativo casu est responsum ad “Quot dies mensis Martius longus est?” seu “Quam longus est Martius mensis?” quaestionem (A&G §423 “…time how long by the accusative”).
Gratias tibi ago Adriani! You gave me the info I was looking for plus some! Thank you for that link as well.