Question 890044
<pre>
First we determine how many terms, n.

{{{a[n]}}}{{{""=""}}}{{{a[1]+(n-1)d}}}

where {{{a[1]=2}}}, {{{a[n]=59}}}, {{{d=5-2=8-5=3}}}, 

{{{59}}}{{{""=""}}}{{{2+(n-1)3}}}

{{{59}}}{{{""=""}}}{{{2+3n-3}}}

{{{59}}}{{{""=""}}}{{{3n-1}}}

{{{60}}}{{{""=""}}}{{{3n}}}

{{{20}}}{{{""=""}}}{{{n}}}

Now we use the sum formula:

{{{S[n]}}}{{{""=""}}}{{{expr(n/2)(a[1]+a[n])}}}

{{{S[20]}}}{{{""=""}}}{{{expr(20/2)(2+59)}}}

{{{S[20]}}}{{{""=""}}}{{{(10)(61)}}}

{{{S[20]}}}{{{""=""}}}{{{610}}}

Edwin</pre>