nhan dip nam hoc moi, chuong trinh "Toyota cung em hoc an toan giao thong" tang cac ban hoc sinh khoi lop IV va khoi V truong em 450 chiec mu bao hiem. Sau khi chuong trinh tang them cho khoi V 50 chiec mu nua thi so mu cua khoi IV bang 2/3 so mu cua khoi V. Hoi luc dau khoi V duoc tang bao nhieu mu bao hiem?