Find S12 for the series 2 + 5 + 8 + ...

2+5+8+11+14+17+20+23+26+29+32+35

Hi, I'm pretty sure by S12 you mean the sum of all the 12 terms in the series 2 + 5 + 8 + ...

Then, first you find the pattern:

5 - 2 = 3

8 - 5 = 3

This is an arithmetic series with a common difference of 3. Next, we find the last term, or the 12th term.

A12 = A1 + (n - 1) d

A12 = 2 + (12 - 1) 3

A12 = 35

Since, we know the first and last terms of the series, we could find the sum by this formula:

S = (n/2) * (A1 + A12)

S = (12/2) * (2 + 35)

S = 222

The answer is 222.