2.
program Tin_hoc;
uses crt;
var i,tong:integer;
begin
clrscr;
tong:=0;
for i:= 1 to 20 do i mod 2 = 0 then tong:=tong + i;
writeln('Tong cac so chan tu 1 den 20 la: ',tong);
readln;
end.
3.
program Tin_hoc;
uses crt;
var i,tong:integer;
begin
clrscr;
tong:=0;
for i:= 1 to 20 do i mod 2 = 1 then tong:=tong + i;
writeln('Tong cac so chan tu 1 den 20 la: ',tong);
readln;
end.