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 encrypt key or encrypt passphrase
Explanation/Answer:
Data can be put into more than one cell (Excel), which should be an important key to your answer. In SEVERAL CELLS AT THE SAME TIME or more. The data can be entered in dates, text, times, or numbers. Formatting the data can be done in a possibility of ways.