I will live in Montmartre. Can I reach La Défense with "Ticket t+"?
You can take Metro 1 from anywhere in Paris to La Défense Grande Arche using a single ticket. Upon arrival, be sure to exit using Metro exit turnstiles as the Ticket t+ won't let you exit by RER exit gates. This is only a possibility when at times the station authorities open barriers normally separating the two systems allowing freer flow of foot traffic in and out of the system, usually during rush hours.