On an average what percentage of games are won by a player 100 points stronger than his opponent?

64% according to: Calculator for

### Theoretical Probability of Winning Based on ELO Ratings:

http://www.bobnewell.net/nucleus/bnewell.php?itemid=279

How much does his rating change if he has been playing for a long time in the FIDE system?

See FIDE.com for an explanation of how they calculate ratings. The experience factor or K factor is something that recently changed. https://en.wikipedia.org/wiki/Elo_rating_system

At what rating difference does the number of points gained from the higher rating player become zero?

Depends on what system you are using. ELO, Glicko, etc.

See also:

http://en.chessbase.com/post/the-elo-rating-system-correcting-the-expectancy-tables

On an average what percentage of games are won by a player 100 points stronger than his opponent?

How much does his rating change if he has been playing for a long time in the FIDE system?

At what rating difference does the number of points gained from the higher rating player become zero?