What Michael said, except that it isn't a case of "an attendant <U>can</u>" sell you a combo ticket - it's automatic. You don't have to ask for it.

Every RER ticket to CDG is valid from any M&eacute;tro or RER station in Paris to the airport - the <I>correspondances</i> between the two networks aren't even gated. This is equally true of tickets from Paris to Versailles and Disneyland.

But the issue is going from Paris to CDG.

More clarification on the combo ticket...it isn't a combo actually.

Buying a ticket for the RER gets you access to the metro on that same journey. No need to ask, it just comes w/ the ticket.

mdtravel,
<i>it just comes w/ the ticket.</i>

Not from Paris. My impression is that you purchased two tickets--a metro ticket and a ticket for the RER. You could have purchased only one.