Hỏi lớp có bao nhiêu học sinh khá

$$\begin{gathered} \mathrm{mot} \mathrm{lop} \mathrm{co} 40 \mathrm{hoc} \sinh ,\mathrm{trong} \mathrm{do} \mathrm{co} 40 \raisebox{1ex}{$\mathrm{o}$}\!\left/ \!\raisebox{-1ex}{$\mathrm{o}$}\right. \mathrm{la} \mathrm{hoc} \sinh \mathrm{gioi},20\raisebox{1ex}{$\mathrm{o}$}\!\left/ \!\raisebox{-1ex}{$\mathrm{o}$}\right. \mathrm{la} \mathrm{hoc} \sinh \mathrm{trung} \mathrm{binh} \\ \mathrm{con} \mathrm{lai} \mathrm{la} \mathrm{hoc} \sinh \mathrm{kha} \mathrm{khong} \mathrm{co} \mathrm{hoc} \sinh \mathrm{yeu}.\mathrm{Hoi} \mathrm{lop} \mathrm{co} \mathrm{bao} \mathrm{nhieu} \mathrm{hoc} \sinh \mathrm{kha} \end{gathered}$$