If 5 spiders can catch five files in five minutes, how many files can hundred spiders catch in 100 minutes ?

Let the required number of chairs be x.
Then, More spiders, More flies (Direct proportion)
More time, More flies (Direct proportion)
\[\left. \begin{gathered} \,\,\,{\text{Spiders 5}}:100 \hfill \\ {\text{Minutes 5}}:100 \hfill \\ \end{gathered} \right\}::5:x\]
$$\eqalign{ & \therefore {\text{ }}5 \times 5 \times x = 100 \times 100 \times 5 \cr & \Leftrightarrow x = \frac{{\left( {100 \times 100 \times 5} \right)}}{{\left( {5 \times 5} \right)}} \cr & \Leftrightarrow x = 2000 \cr} $$