I3.1 The monthly salaries of 100 employees in a company are as shown:
\begin{tabular}{|l|c|c|c|}
\hline Salaries (\$) & 6000 & 4000 & 2500 \\
\hline No. of employees & 5 & 15 & 80 \\
\hline
\end{tabular}

If the mean salary is $\$ m$, find $m$.
$\begin{aligned} m & =\frac{6000 \times 5+4000 \times 15+2500 \times 80}{5+15+80} \\ & =\frac{290000}{100}=2900\end{aligned}$