Question

What is the sum of the first 35 terms in the series 7 + 9 + 11 + ...?

Answer 1

First find the 35th number in the series using the formula:
an = a1 + (n - 1)d
a1 = first number in the series
d = difference between successive number
n = number of terms
a35 = 7 + (35 - 1)2
a35 = 7 + (34)2 
a35  = 7 + 68 = 75.
Therefore, the 35th term is 75.
To find the sum of the first 35 numbers, use the formula:
Sn = n(a1 + an) / 2
Sn = 35(7 + 75) / 2
Sn = 2870 / 2 = 1,435.
Therefore, the sum of the first 35th term is 1,435.
The correct answer is D.

Answer 2

The answer is d 
Hope this helps :)