Alg 2
posted by Schuyler .
What is the sum of a 12term arithmetic sequence where the last term is 13 and the common difference is 10?

Schuyler, the sum of the 12 term aritmetic progression is 816

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+(n1)d so 13+(121)10
L=123
Then I used this formula:
Sn=n/2(a+L)
Sn=12/2(13+123)
Sn=6 Times 136
Sn=816