It might be interesting to see if we can discover a pattern here.
Note
Three elements....two at time (1,2) (1,3) (2,3)....sum = 12
Four elements .... two at a time (1,2) (1,3) (1,4) (2,3) (2,4) (3,4) .....sum = 30
Five elements....two at a time (1,2) (1,3) (1,4) (1,5) (2,3) (2,4) (2,5) (3,4) (3,5) (4,5) ....sum = 60
Note that for N elements taken 2 at a time......the pattern of sums seems to be
(N - 1) ( N ) ( N+ 1) / 2
So....for 6 elements taken 2 at a time.....the sum should be
(5) (6) (7) / 2 = 210 / 2 = 105
Verify for yourself that this is true.......!!!!!!
