I am visiting Paris and will stay there for about a week. I will visit the exhibition in Villepinte (Parc des expositions is the station).

I will travel from GARE DU NORD to PARC DES EXPOSITIONS between the 20 of October (saturday) to the 25 of October (Thursday). I will travel by morning to the exhibiton at parc des expositions, and arrive back to Gare du nord every evening.

Which is the cheapest way to travel back and forth during these days? Since I am a visitor in Paris I think the Zone-system could be the cheapest, what do you think?

Is it true that I will pay from 20-21 and then for a new week for 22 to 25 of october?