Posted by **Schuyler** on Monday, June 20, 2011 at 10:02am.

What is the sum of a 12-term arithmetic sequence where the last term is 13 and the common difference is -10?

- Alg 2 -
**Raymond**, Monday, June 20, 2011 at 10:27am
Schuyler, the sum of the 12 term aritmetic progression is 816

- Alg 2 -
**Raymond**, Monday, June 20, 2011 at 11:17am
Schuyler, in order to solve your problem I had to turn it around (Gloria Estefan?). You said the last term was 13...I made it the first term. You said the common difference was a -10...I made it a +10.

Now I had to find the last term so I used this formula: L=a+(n-1)d so 13+(12-1)10

L=123

Then I used this formula:

Sn=n/2(a+L)

Sn=12/2(13+123)

Sn=6 Times 136

Sn=816

## Answer this Question

## Related Questions

- Algebra - True or False 1. – 5, – 5, – 5, – 5, – 5, … is an arithmetic sequence...
- arithmetic sequence - the 40th term of an arithmetic sequence is equal to the ...
- Maths - 1..The first 2 terms of a geometric progression are the same as the ...
- Arithmetic Sequence - Given the third term of an arithmetic sequence less than ...
- mathematics - 1.1 the third term of an arithmetic sequence is 8 and the 15 term ...
- Precalculus - The 8th term in an arithmetic sequence is 5, and the sum of the ...
- math - find the rule for the Nth term of the arithmetic sequence. 11/2, 25/6, 17...
- math - The 3rd term in an arithmetic sequence is 12, the 7th term is 24, a) How...
- Mathematics : Arithmetic Sequence - The 5th term and the 8th term of an ...
- Math - A sequence is formed by adding together the corresponding terms of a ...

More Related Questions