Each of the 20 people has 19 other people to communicate to. If you add that all up you get 20*19 paths, but then each path is counted twice (back and forth), so we divide this by 2. 20*19/2 = 190.
The general forumula is n(n-1)/2
The class clock type was designed to implement the time of day in a program. Certain applications, and additions to hours, minutes, and seconds, might require you to start at the time zone.
