Hey!

I'm just wondering if you are able to buy a ticket at the Châtelet Les Halles station so that you can travel from the station to Antony and to Orly without purchasing a ticket at Antony? I and my dad are going to Paris tomorrow, and I'm thinking of just using single one way tickets. How do these work?
We arrive at CDG Airport, and from what I've read it seems easier to get around there, but then we're travelling home from Orly.

Thanks!