Question 847912
{{{a[n]=a[1]+(n-1)*d}}}   d = -1
{{{a[n]=30 +(n-1)*-1=5 }}}
{{{a[n]=30 - n + 1 =5 }}}
       {{{n = 26}}}
{{{S[n]=(n(a[1]+a[n]))/2}}}}
{{{S[26]=(26(30+5))/2}}}}