Question about a project in Italy?

N*(N-1/2) Project Managment Formula Question?

• Could you please explaing why the answer is 18. The Project Manager has 4 people reporting to him. Three more people are added to the project. How many communication channels were added to the project? The formula is N*(N-1)/2 First calculate the number of communication channels based on the existing team 4 and the Project mang. = 5. That is 10 communication channels. Next, calculate the numbre of communication channels with the new people added. This is 28 communication channels. Finally, subtract the difference (28-10=18) I still don't understand how the answer is 18

• Answer:

  Let call A, B, C and D the 4 first people E,F,G the three others and M the manager. The communication channels are : A-B, A-C, A-D, B-C, B-D, C-D, A-M, B-M, C-M and D-M so 10 in total If you add 3 people E, F,G you have added now : A-E, A-F, A-G, B-E, B-F, B-G, C-E, C-F, C-G, D-E, D-F, D-G, E-F, E-G, F-G, M-E, M-F, M-G so 18 added and 28 in total It is also how to select 2 people between n : C(2,n) = n (n-1)/2 = 8*7/2 = 28