In this case, the number of students refers to frequencies.
To find the mean, we have to use the following formula
[tex]\begin{gathered} \bar{x}=\frac{\Sigma(x\cdot f)}{N}=\frac{65\cdot4+70\cdot1+75\cdot7+80\cdot5+85\cdot8+90\cdot3+95\cdot4+100\cdot1}{33} \\ \bar{x}=\frac{260+70+525+400+680+270+380+100}{33} \\ \bar{x}=\frac{2685}{33} \\ \bar{x}\approx81.4 \end{gathered}[/tex]
Hence, the mean is 81.4.
