[lmikle]

как-то так:

Код:

var
  I, J : Integer;
  S : Double;
begin
  For I := 0 To StringGrid1.RowCount-1 Do
    Begin
      S := 0;
      For J := 0 To StringGrid1.ColCount-2 Do
         S := S + StrToFloat(StringGrid1.Cells[I,J]);
      StringGrid1.Cells[I,StringGrid1.ColCount-1] := FloatTostr(S);
   End;