Question 87314
It appears this sequence is an arithmetic one (since we simply add 10 each time to get from term to term).

So the arithmetic sequence would be 

{{{a[n]=10n+7}}}


So plug in {{{a[n]=107}}} to find out how many terms there are:


{{{107=10n+7}}} plug in {{{a[n]=107}}}


{{{100=10n}}} Subtract


{{{100/10=n}}} Divide


{{{n=10}}} Reduce


Since we start off at {{{n=0}}} there are 11 terms


In order find the sum of an arithmetic sequence, simply use this formula


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


{{{S=(11/2)(7+107)}}} Plug in {{{a[1]=7}}}, {{{a[n]=107}}}, and {{{n=11}}}


{{{S=(11/2)(114)}}} Add


{{{S=627}}} Multiply


So 11 terms of this sequence adds up to 627