Bài 1:

program chiahetcho3;

uses crt;

var i,d:word;

begin

     clrscr;

     d:=0;

     for i:=1 to 50 do 

          if i mod 3=0 then d:=d+1;

     write('Tu 1 den 50 co ',d,' so chia het cho 3');

     readln;

end.

Bài 2:

program songuyento;

uses crt;

var n,i,d:integer;

begin

     clrscr;

     write('Nhap so N can kiem tra: ');  readln(n);

     if n<2 then write(n,' khong phai so nguyen to')

     else

          begin

               d:=0;

               for i:=2 to n div 2 do

                    if n mod i=0 then d:=d+1;

               if d=0 then write(n,' la so nguyen to')

               else write(n,' khong phai so nguyen to');

          end;

     readln;

end.

Bài 1:

Program thichvaydo;

Uses crt;

Var dem,i: byte ;

Begin

Clrscr;

For i:=1 to 50 do

If i mod 3 = 0 then inc(dem);

Write('cac so chia het cho 3 tu 1 den 50 la',dem);

Readln

End.

Bài 2:

Program dacony;

Uses Crt;

Var n,d,k:longint;

Begin Clrscr;

write('n=');

Readln(n);

k:=0;

For d:=1 to n do

If n mod d = 0 then

k:=k+1;

If k=2 then

write ('n chinh la so nguyen to');

Readln;

End.