1. tim ket qua cua phep nhan.
A = 33...3 * 99...9
--------- ----------
100so3 100so9
2.cho tap hop cac so tu nhien khong vuot qua 100 chia co 7 du 3
a, hay viet tap hop A = 2 cach
b, tinh tong cac phan tu cu A
c, tinh so chu so dung de viet cac tap hop A
3. nguoi ta danh so trang cua mot quyen sach = day so 1;2;3........quyen sach day 300 trang.hoi
a, tinh so chu so dung de danh so trang sach
b, chu so 659 thuoc trang nao va chu so may