Question

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?

• A. 9
• B. 10
• C. 11
• D. 12

Answer 1

Answer: (D)

12

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)
$\begin{array}{c}Pumps4:3\\ Days1:2\end{array}\}::8:x$
$\therefore 4\times 1\times x=3\times 2\times 8$
$\Rightarrow x=\frac{(3\times 2\times 8)}{\left(4\right)}$
$\Rightarrow x=12$