Question 1151010
Consider the way that Gauss showed us how to sum an arithmetic sequence. 

Your example is an arithmetic sequence so there is some number d that you add to each term to obtain the next term. 

The middle term of a {{{15}}} term sequence is {{{92}}}; so, this is the {{{8}}}th term. 

The last term is {{{7}}} terms further along in the sequence so it is {{{92 + 7d}}}. 

Likewise the first term is {{{7}}} terms before the {{{8}}}th term so it is {{{92 - 7d}}}. 

Thus the sum of the first and last term is {{{92 - 7d + 92 + 7d = 92 + 92 = 184}}}

now use Gauss' technique to find the sum of the sequence

{{{S=(n/2)(a[1]+a[n])}}} where {{{n}}}=number of terms, {{{a[1]}}}=first term, and {{{a[n]}}}=last term

{{{S=(15/2)(184)}}}

{{{S=15*92}}}

{{{S=1380}}}