Bài 1:
program TenCT;
uses crt;
var a,b,c,d:integer; tb:real;
begin
  clrscr;
  write('Nhap so a= '); readln(a);
  write('Nhap so b= '); readln(b);
  write('Nhap so c= '); readln(c);
  write('Nhap so d= '); readln(d);
  writeln;
  tb:=(a+b+c+d)/4;
  writeln('Trung binh cua 4 so do la: ',tb:0:1);
  readln;
end.
Bài 2:
program TenCT;
uses crt;
var n:longint; 

  function nto(x:longint): boolean;
  var t,i:integer;
  begin
    if (x<2) then exit(false);
    if (x=2) or (x=3) then exit(true);
    t:=trunc(sqrt(x));
    for i:=2 to t do
      if (x mod i=0) then exit(false);
    exit(true);
  end;

begin
  clrscr;
  write('Nhap so nguyen n= '); readln(n);
  if nto(n) then writeln(n,' la so nguyen to')
    else writeln(n,' khong phai la so nguyen to');
  readln;
end.