1.

var i,s,n1,n2:longint;

begin

write('Nhap n1: '); readln(n1);

write('Nhap n2: '); readln(n2);

for i:=n1 to n2 do

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

write('Tong la: ',s);

readln;

end.

2.

var i:longint;

begin

for i:=100 downto 5 do

if i mod 5 = 0 then write(i,' ');

readln

end.

3. 

var x,n,s,i:longint;

function lt(x,n:longint):longint;

var kq,j:longint;

begin

kq:=1;

for j:=1 to n do

kq:=kq*x;

exit(kq);

end;

begin

write('Nhap x: '); readln(x);

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

for i:=1 to n do

s:=s+lt(x,i);

write('Tong la: ',s);

readln

end.

Bài 1:
---
Program BTT;
Uses crt;
Var n1,n2: longint;
    s,i: longint;
Begin
        Clrscr;
        Write('Nhap n1 va n2: '); Readln(n1,n2);
        s:=0;
        For i:=n1 to n2 do
                If i mod 2 = 1 then s:=s+i;
        Write('S = ',s);
        Readln
End.
---
Bài 2:
---
Program BTT;
Uses crt;
Var i: byte;
Begin
        Clrscr;
        For i:=100 downto 5 do
                If i mod 5 = 0 then Write(i,' ');
        Readln
End.