Đáp án Olympic tin Bắc Giang

Bài 1
Var i,n:integer;
s:longint;
Function nt(a:integer):boolean;
Var b,dem:integer;
Begin
dem:=0;
For b:=1 to a do
if a mod b = 0 then dem:=dem+1;
if dem = 2 then nt:=true
else nt:=false;
End;
BEGIN
Write(`Nhap N: `); Readln(n);
If ((n mod 2) <> 0) then
for i:= 2 to n do
if nt(i) then s:=s+i;
if n mod 2 = 0 then
for i:=1 to n do
if (i mod 2) <> 0 then s:=s+i*i;
Writeln(`Tong S=`,s);
readln;
END.
Bài 2

Var
i,j,k,n,x,y,z,dem: integer;
BEGIN
Write(`Nhap so tien can rut ( n<= 10000): `); readln(n);
Write(`Nhap 3 loai tien ma may co (x,y,z<=500) : `); readln(x,y,z);
For i:=0 to n div x do
for j:=0 to n div y do
for k:=0 to n div z do
if i*x +j*y +k*z = n then
begin
Dem:=dem+1;
Writeln(`Cach `,dem,`: So tien loai `,x,`; `,y,`; `,z,`; lan luot la: `,i*x,`; `,j*y,`; `,k*z,`.`);
end;
if dem= 0 then Write(`Khong co cach nao de rut dung so tien yeu cau`)
else Writeln(`Co tat ca `,dem,` cach rut tien`);
readln;
END.
Bài 3
uses crt;
Var
i,t,k1,k2: integer;
j,g: char;
s1,s2: String;
BEGIN
Write(`Nhap xau ky tu : `); Readln(s1);
For i:=1 to length(s1) do s1[i]:=Upcase(s1[i]);
For i:=1 to length(s1) do
For j:=`A` to `Z` do
Begin
if j=s1[i] then
begin
t:= (k1+5) mod 26;
k2:=0;
for g:=`A` to `Z` do
begin
if k2=t then s2:=s2+g;
k2:=k2+1;
end;
end;
k1:=k1+1;
end;
Write(` Xau ky tu tren duoc ma hoa la: `,s2);
Readln;
END.