SOLUTION: what is the series summation notation of 5,10,15,20,25?

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Question 706680: what is the series summation notation of 5,10,15,20,25?

Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
Try this:

(5+10+15+20+25)+(25+20+15+10+5)
= 5%2A%2830%29
=5%2A%285%2B25%29

The sequence was repeated but backwards to create that sum. We want HALF of that sum, so:
WANT: highlight%285%2A%285%2B25%29%2F2%29
Note, this is for an arithmetic sequence of sequential terms being summed.
That is the number of terms being summed, the use of the first and last term to be summed, and division by 2.