7th Grade Math
posted by John :) on .
Linda's teacher divided the class into groups of five and required each member of a group to meet with every other member of that group. How many meetings will each group have?

I know the answer is 10, but the problem is I can't find out the formula :/ if I only show the answer I won't get any credit and it'll be marked wrong.

5 per group.
person x = 1st person meeting everyone
x  1, x  2, x  3, x4 (no x  5 because he/she is 5th person).
Meeting count:4
second person meeting everyone = y
y  1, y 2, y  3,
(no y 4 or y  5 because he/she already met with person x and cannot meet with himself)
Meeting count: 7
third person meeting everyone = z
z  1, z  2
z has already met with y, z has already met with x, z cannot meet him/herself.
Meeting count: 9
fourth person meeting everyone = k
k 1
k has already met with x,y, and z. k cannot meet with himself
Meeting count:10
everyone has met with each other 
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