How Many Handshakes?

1) There will be a total of 45 handshakes due to the fact ever person will have to shake their hand once with each person. A-B B-C A-C B-D D-A C-D

2)There will be a total of 55 handshakes because there will be 10 more handshakes added if another person joined. Each person would have their number of handshakes increased for another joining the room.
                                                                 
3)There will be a total of 90 hand shakes between each student because you double the number of hand shakes exchanged between 10 students.