Nguoi khach co the hoi nguoi dau tien anh ta gap : " Ngai co phai la nguoi cua thanh pho nay khong ? "

Neu o thanh pho A, thi luon nhan duoc cau tra loi la : " Vang " va neu dang o thanh pho B, thi cung nhan duoc cau tra loi la : " Khong "

That vay , khi o thanh pho A, nguoi ta se tra loi du khach la : " Vang " con nguoi tra loi o thanh pho B, thi se noi doi va cung noi la vang. Tu day du khach co the biet dau la thanh pho A va dau la thanh pho B !

Bai toan da duoc chung minh !