Need help

1. A computer technician is to repair 5 out of 7 computers in the Laboratory room.

(a) How many choices has he?

(b) How many if he must repair the first 2 computers?

2. (a) In how many ways can a sales lady with 15 associates invite 7 of them to attend the party?,

(b) if 3 of them are neighbors from far away and will not attend separately?, and

(c) if 3 of them will not attend together?