Question

What is the sum of the arithmetic sequence 149, 135, 121, …, if there are 28 terms?

Answer 1

I needed my brother to help me with this one,so here is the answer.
The common difference is -14. 

Let's simplify this by expressing each term as 
163 - 14n 
where n is the number of the term. 

Then the sum of the 28 terms is 
28 * 163 - 14 (1+2+3+...+28) 
= 4,564 - 14 * 28 * 29 / 2 
= -1,120