[tex]Notam: \\ x=numarul~notelor~de~9. \\ y=numarul~notelor~de~7 \\ ------------ \\ \\ x= \frac{1}{5} \cdot y \\ y=x+8 \\ \\ \Rightarrow x= \frac{1}{5}(x+8) ~~~~~~~~~~| \cdot 5 \\ 5x=x+8 \\ 5x-x=8 \\ 4x=8 \Rightarrow x=2. \\ \\ y=x+8=2+8=10.[/tex]
[tex]\underline{Solutie}:~s-au~obtinut~10~note~de~7~si~2~note~de~9.[/tex]