Question 859198
<pre><font face = "Tohoma" size = 3 color = "indigo"><b> 
Hi, Previously Posted
{{{S[n]= (n/2)(2*a[1]+ (n-1)d)}}}
{{{S[n]= (n/2)(24 + (n-1)5) = 345}}}
          n(19 + 5n) = 690
          5n^2 + 19n - 690 = 0
{{{n = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}} 
{{{n = (-19 +- sqrt( 14161 ))/(10) }}} Tossing out negative solution
{{{n = (-19 +- 119)/(10) }}}
      n = 10