3 pumps, working 8 hours a day, can empty a tank in 2 days. How many hours a day must 4 pumps work to empty the tank in 1 day?

Solution(By Examveda Team)

Let the required number of working hours per day be x.
More pumps, Less working hours per day (Indirect Proportion)
Less days, More working hours per day (Indirect Proportion)
\[\left. \begin{gathered} {\text{Pumps 4}}:3 \hfill \\ {\text{Days}}\,\,\,\,\,\,\,\,{\text{1}}:2 \hfill \\ \end{gathered} \right\}::8:x\]
$$\eqalign{ & \therefore 4 \times 1 \times x = 3 \times 2 \times 8 \cr & \Rightarrow x = \frac{{ {3 \times 2 \times 8} }}{{ 4 }} \cr & \Rightarrow x = 12 \cr} $$