Originally Posted by stimpy

I'm not sure as I don't have to pay full price. Maybe around €10 or so from the airport to Noisy. If you don't have a chipped credit card from an acceptable issuer, or enough Euro coins, you'll have to go to the human ticket booth to purchase a ticket. The human line is often long and slow as first timers ask a lot of questions. Just follow the signs that say Trains to Paris after you get out of the baggage area.

Then when you get to Chatelet, look for the red RER A signs, make sure you choose the right direction and the right train by looking at the posted map as you go down the stairs and looking at the monitor or display board next to the tracks to see if the next train stops at your stop.