4 mat-weavers can weave 4 mates in 4 days. At the same rate, how many mats would be woven by 8 mat-weavers in 8 days ?

Explanation:-

Let the required number of mats be x
More weavers , More mates ( Direct proportion )
More days, More mats ( Direct proportion )
$$\left. \begin{gathered} {\text{Weavers }}4:8 \hfill \\ \,\,\,\,\,\,\,\,{\text{Days }}4:8 \hfill \\ \end{gathered} \right\}::4:x$$
$$\eqalign{ & \therefore 4 \times 4 \times x = 8 \times 8 \times 4 \cr & \Leftrightarrow x = \frac{{\left( {8 \times 8 \times 4} \right)}}{{\left( {4 \times 4} \right)}} \cr & \Leftrightarrow x = 16 \cr}$$