Lop 6B co 45 HS hoc luc duoc chia lam 3 loai: Gioi, kha, trun binh. So HS trung binh chiem \(\frac{2}{9}\)so HS ca lop, so HS kha bang 60% so HS con lai
a) Tinh so HS moi loai
b) Tinh ti so giua cac HS gioi va HS trung binh
c) So HS gioi chiem bao nhieu phan tram hoc sinh cua ca lop?