The first and last terms of a 10-term arithmetic series are listed in the table. What is the sum of the series?

Term Number Term

1 3

10 75

195

390

780

1125

The arithmetic sequence general formula is an = a1 + d * (n-1) where d is the arithmetic difference and n is an integer. In this case, upon derivation, the formula that represents the sum of the series is S = (a1 + an) * (n/2). Substituting, S = (3+75) * (10/2) equal to 390