What is the sum of the arithmetic sequence 3, 11, 19 ..., if there are 26 terms?

Question

What is the sum of the arithmetic sequence 3, 11, 19 ..., if there are 26 terms?
Choose one answer.
A. 1,222
B. 1,261
C. 2,486
D. 2,678

Answer 1

d=8

a1 =3

n=26

an = a1 +d(n-1)

a26 = 3 +8(25) = 3+200 = 203 = last term = 26th term

sum = half number of terms times sum of 1st and last terms

s26 = (26/2)(3+203) = 13(206) = 2678

D is correct