Question 448455
  <pre><font face = "Tohoma" size = 4 color = "indigo"><b> 
Hi,
Arithmetic series/6 terms: {5,8,11,...20} {{{highlight(d=3)}}}
{{{S[n]=(n/2)(2*a[1]+ (n-1)d)}}}
{{{S[6]=(6/2)(2*5+ 5*3) = highlight(75)}}}