1)

uses crt;
 var a, tong : real ;
  begin
   clrscr;
    write('Nhap tong so tien: ');
     readln(a);
    if a >= 1000000 then tong := a*((100-15)/100)
     else tong := a ;
    writeln('Hoa don : Tien thanh toan la :',tong:2:2);
     end.

2)

uses crt;
 var n,s,i : integer ;
  begin
   clrscr;
    write('N=');
     readln(n);
 for i := 2 to n do 
  s := s + i ;
   writeln('S=',s);
    end.

3)

uses crt;
 var n,i : integer ;
 p : real ;
  begin
   clrscr;
    write('N=');
     readln(n);
     p := 1 ;
 for i := 3 to n do 
  p := p * i ;
   writeln('S=',p:0:0);
    end.

- Chương trình 1 :

uses crt;

var t : real;

begin

clrscr;

write('Nhap tong so tien = '); readln(t);

if t >= 1000000 then t := t * 0.85;

write('Hoa don = ', t : 2 : 0);

readln

end.

- Chương trình 2 :

uses crt;

var i, N, Tong : integer;

begin

clrscr;

Tong := 0;

write('N = '); readln(N);

for i := 2 to N do Tong := Tong + i;

write('Tong la : ', Tong);

readln;

end.

- Chương trình 3 :

uses crt;

var i, N, Tich : integer;

begin

clrscr;

Tich := 1;

write('N = '); readln(N);

for i := 3 to N do Tich := Tich * i;

write('Tich la : ', Tich);

readln;

end.