You are project manager and during the course of a project, the number of team members increases form six to ten. How many ADDITIONAL lines of communication channel now exist?

A.
10

B.
35

C.
30

D.
55

Explanation:
lines of communication channel = n(n-1)/2 So answer is 10(10-1)/2 – 6(6-1)/2 = 45-15 = 30