khi tra bai kiem tra mon toan ,co giao noi ;so diem 9 chiem 25% / so diem 10 nhieu hon so diem 9 la 6,25% , nhu vay co 18 ban duoc diem 10 hoac diem 9 ,  tat ca hoc sinh deu nop bai kiem tra . hoi lop do co bao nhieu hoc sinh?