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# 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?

Option :

Explanation:

Solution:
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)
$\begin{array}{c}\text{Pumpu 4}:3\\ \text{Days}\phantom{\rule{thinmathspace}{0ex}}\phantom{\rule{thinmathspace}{0ex}}\phantom{\rule{thinmathspace}{0ex}}\phantom{\rule{thinmathspace}{0ex}}\phantom{\rule{thinmathspace}{0ex}}\phantom{\rule{thinmathspace}{0ex}}\phantom{\rule{thinmathspace}{0ex}}\phantom{\rule{thinmathspace}{0ex}}\text{1}:2\end{array}\right\}::8:x$

$\begin{array}{rl}& \therefore 4×1×x=3×2×8\\ & ⇒x=\frac{\left(3×2×8\right)}{\left(4\right)}\\ & ⇒x=12\end{array}$