Paris local transport question -- ticket options, most economical ticket?

Hello everyone, I am going to be in Paris for 4 days/3 nights. We are two adults and two children. My hotel website says that the closed Train Station is: Chessy Marne la Vallée, and the closest subway station is Noisy - Mont d'Est. (Hotel reception told me that the are on RER A line) I will be travelling... show more Hello everyone,

I am going to be in Paris for 4 days/3 nights. We are two adults and two children. My hotel website says that the closed Train Station is: Chessy Marne la Vallée, and the closest subway station is Noisy - Mont d'Est. (Hotel reception told me that the are on RER A line)

I will be travelling to Paris center daily from the hotel (to visit the typical tourist places) - and I might go to Versailles on one of the days

I am not too sure how the transport system / ticket system in Paris works. Can you please advise what would be the most economical ticket option ? A set of 10 individual tickets ? Or some sort of daily tickets that would allow me to travel from hotel to the center. Request you to share any official websites that can give me more information (in English !) on the routes, fares etc...

We are ok to walk reasonable distances (and in fact, I am keen to walk wherever possible)

Any advise would be highly appreciated.

Thanks
Update: Sincere thanks for all the answers so far...I was going through the official Paris tourism site: http://en.parisinfo.com/paris-map/getting-around/public-transport/guide/public-transport_fares-travel-passes-and-reductions It says, "In the RER, as long as you remain within the city limits, tickets and prices... show more Sincere thanks for all the answers so far...I was going through the official Paris tourism site: http://en.parisinfo.com/paris-map/getting-around/public-transport/guide/public-transport_fares-travel-passes-and-reductions

It says, "In the RER, as long as you remain within the city limits, tickets and prices are identical to the metro (RER stations also have their own ticket offices and machines). If you are travelling beyond the city limits, you need to ensure that you are in possession of a ticket or a pass which covers your whole journey up to your destination in the Ile-de-France region."

As mentioned earlier, my hotel is near Noisy - Mont d'Est (Holiday Inn). Can I buy the carnet - one ticket of which can cover one full journey from hotel to, say, Eiffel Tower (Including a change from RER A to Metro) ? If not, do I need two separate tickets to cover (1) RER A journey from Nosiy - Mont d'Est to Chatelet Les Halles and (2) From Chatelet Les Halles to Eiffel Tower ?
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