What is the sum of the first 20 terms in the arithmetic series?

-6 + (-2) + 2+6 + ...

624

640

654

680

Use sum of arithmetic series:

Sum of n terms = (n/2) (2a + (n - 1) d)

where a is the first term, - 6

d is the common diff, 6 - 2 = 4

and n is the number of terms, 20

Sum of first 20 terms

= (20/2) (2 (-6) + 19 (4))

= 640