ECAT Engineering Exams Quizzes MCQs Quizzes ECAT Engineering Entry Test 2017 Mathematics Sequences and Series

Question:
if a, d and Sn   are the first terms, the common difference and the sum of first n terms of the series , then Sn =

Option A):
n[2a  + (n-1)d]
Option B):
n/2[a  + (n-1)d]
Option C):
a  + (n-1)d
Option D):
n/2[2a  + (n-1)d]

Correct Answer is Option D):
n/2[2a  + (n-1)d]