http://www.paris-travel-guide.info/eiffel-tower-tickets-price/
How to get to Eiffel tower from CDG and back with RER?
I want to know what routes to take etc. for going to the eiffel tower from charles de gaulle and back to the airport from the eiffel tower.
I would also appreciate if you mentioned the ticket prices and how long it would take.
THANKS 
well, there are several routes to take. I would recommend you take line B (its the blue line) from CDG all the way to Saint michel Notre Dame stop. There you can switch to train line C (the yellow line) and get off on Champ de Mars Tour Eiffel station. That should be an approximately 45 minutes ride.
To get back to the airport you can take the same route or can make your own. See the link below. Dont forget to buy an all day pass…it cost 4 euros, I think! Bon vayage!
Bon chance…
“Le Louvre, Notre Dame and the Eiffel Tower” Spo_rt’s photos around Paris, France