Hi Ben (and traveling Paris community),
I think I've got this trip planned out. The only thing I'm "fuzzy" about is getting from CDG (Terminal 1) to our apartment near Trocadero (in between Trocadero and Passy Metro Station).
I know that I'm taking the RER-B Train but my question is will that same ticket allow me to jump onto the Metro or do I need to buy a separate Metro ticket?
Thanks in advance!
The same RER B ticket used at CDG Airport can be used to transfer onto Metro in Paris to complete your trip, anywhere on the entire Metro system. Any turnstiles you encounter while transferring (say at Chatelet or Gare du Nord), you would use the same already-validated ticket. This works for transfers between RER to Metro or Metro to Metro, as long as you're not exiting the system via turnstiles/gates that lead to ground level.
Some stations (especially Chatelet) will have multiple levels of turnstiles as you pass from RER to Metro system, requiring your RER ticket (or Metro ticket / ticket t+) to exit the RER area and enter a Metro area, all the while you're still inside the fare-validated area and your RER/Metro ticket is still valid & required to make these transfers.