What is the sum of the first 100 terms of this sequence: 5, 11, 17, 23...?
I know how to calculate this but according to a site, my calculations are wrong. I did 5 + 6*99 which indicates the final term. Adding the final term to the first term 599+5 and dividing that by 2, would be the average. The number of terms as stated is 100, so the answer should be 302 * 100, but according to the site, that's not the answer, so I don't know what I did wrong here.
The sum of an arithmetic sequence is given by where
- is the number of terms
- which is the first term
- is the common difference (between terms)
You are told that and it's not hard to see that . Now all that's left is to find the common difference and then plug into the formula at the top of this post.
L'edit: Google Calculator gives 30,200 as a answer which is evidently the same as 302*100