Bài 1: 

program h247;

uses crt;

var n,i,s: longint;

begin

write('Nhap n '); readln(n);

s:=0;

for i:=1 to n do s:=s+i;

write('Tong la ',s);

readln;

end.

Bài 2:

program h247;

uses crt;

var n,i,t: longint;

begin

write('Nhap n '); readln(n);

t:=1;

for i:=1 to n do t:=t*i;

write('Tich la ',t);

readln;

end.

Bài 3:

program h247;

uses crt;

var i,tl: byte;

begin

tl:=0;

for i:=1 to 20 do

if i mod 2 <>0 then tl:=tl+i;

write('Tong le ',tl);

readln;

end.

Bài 4: 

program h247;

uses crt;

var i,tc: byte;

begin

tc:=0;

for i:=1 to 20 do

if i mod 2=0 then tc:=tc+i;

write('Tong chan ',tc);

readln;

end.

Bài 1:

uses crt;
var n,kq,i:integer;
begin
        clrscr;
        write('Nhap n: '); readln(n);
        for i:=1 to n do
                kq:=kq+i;
        write('Tong la: ',kq);
        readln;
end.

Bài 2:

uses crt;
var n,kq,i:longint;
begin
        clrscr;
        kq:=1;
        write('Nhap n: '); readln(n);
        for i:=1 to n do
                kq:=kq*i;
        write('Tong la: ',kq);
        readln;
end.

Bài 3:

uses crt;
var kq,i:longint;
begin
        clrscr;
        for i:=1 to 20 do
                if i mod 2 = 0 then kq:=kq+i;
        write('Tong la so chan 1 den 20 la: ',kq);
        readln;
end.

Bài 4:

uses crt;
var kq,i:longint;
begin
        clrscr;
        for i:=1 to 20 do
                if not i mod 2 = 0 then kq:=kq+i;
        write('Tong la so chan 1 den 20 le: ',kq);
        readln;
end.