Find the sum of the series ∑12i=1(3i-1)

Sum i=1 to 12 of (3i-1):

2+5+...+35

12 terms; sum of first and last terms is 37.

Sum = (number of terms) times (average of all the terms)

For an arithmetic sequence, the average of all the terms is the average of the first and last terms:

Sum = (number of terms) times (average of first and last terms)

The year before the 10s so it was like when caveman were alive