The score at rugby - Lycée Emmanuel d'Alzon (Nîmes)

 In a simplified version of a rugby game, players are able to score 3 or 5 points only. In these conditions, they can score 8 points but not 7.
1. What are the scores a team can get?
2. Can we get all the integer numbers from a certain number of points?
3. What happens when players follow the regular rules of rugby (with the conversion of trials)?