Probability and statistics

1.- A person places on a shelf in a bookstore 6 books on philosophy, 4 on chemistry and 8 on history. How many ways can books be accommodated if the books must be separated by Subjects.

2.- A football team participates in a tournament in which it will have to play 12 games throughout the season How much can the team finish the season with 7 wins, 3 losses and 2 draws?

3.-A student wants to organize a study circle for the Probability exam with some of his friends.Due to the size of his house, he can only invite 11of his 20friends. How many ways can you select guests?

4.- How many different products of three factors each; can be obtained with the numbers: 2; 5; 17; 19; 23 and 31?