По теории вероятности подсчитайте простое

procedure TForm1.Button1Click(Sender: TObject);
var
  n, n3p,
  k0, k1, k2, k3, k4, k5: integer;
  p: extended;
begin
  n := 0;
  n3p := 0;
  for k0 := 0 to 50 do
  for k1 := k0 + 1 to 51 do

  for k2 := 0 to 50 do
  if ( k2 <> k0 ) and ( k2 <> k1 ) then
  for k3 := k2 + 1 to 51 do
  if ( k3 <> k0 ) and ( k3 <> k1 ) then

  for k4 := 0 to 50 do
  if ( k4 <> k0 ) and ( k4 <> k1 ) and
     ( k4 <> k2 ) and ( k4 <> k3 ) then
  for k5 := k4 + 1 to 51 do
  if ( k5 <> k0 ) and ( k5 <> k1 ) and
     ( k5 <> k2 ) and ( k5 <> k3 ) then begin
    inc( n );
    if ( k0 mod 13 = k1 mod 13 ) and ( k2 mod 13 = k3 mod 13 )
       and ( k4 mod 13 = k5 mod 13 ) then
      inc( n3p );
  end;
  p := n3p / n;
  memo1.Lines.Add( inttostr( n ) );
  memo1.Lines.Add( inttostr( n3p ) );
  memo1.Lines.Add( floattostr( p ) );
end;