SOLUTION: Find the sum of the first 12 terms of arithmetic sequence with a common difference of -5 if its 23rd term is 556.

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Question 1141173: Find the sum of the first 12 terms of arithmetic sequence with a common difference of -5 if its 23rd term is 556.
Answer by josgarithmetic(39618) About Me  (Show Source):
You can put this solution on YOUR website!
Common Difference -5 as given

If first term is A, then A%2B%28-5%29%2823-1%29=556
A=666}}
-
12th term is 666-5(11)=500
Sum asked for is (12/2)(666+500) from the summation formula for Arithmetic Series.

6996