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?
9
10
11
12
Explanation:
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)
$\therefore$ 4 x 1 x $ x $ = 3 x 2 x 8
| $\Rightarrow x $ =$ \dfrac{(3 \times 2 \times 8)}{(4)} $ |
$\Rightarrow x $ = 12.