Mot ong tuong cam binh di dep giac.Ong cho binh xep thanh hang 9 thi thay thieu mot nguoi . Thay vay ong lai cho binh xep hang 8 thi lai thay thieu mot nguoi. Ong tiep tuc cu cho binh xep hang 6,5,4,3,2hay hang 10 thi van thay thieu mot nguoi .Hoi so binh cua ong la bao nhieu?Biet so luong binh cua onh be hon5000.