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?

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)
Pumps 4 : 3
⟩ : : 8 : x
Days 1 : 2
4 × 1 × x = 3 × 2 × 8
x = 12
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Shortly:
Pumps 4 : 3 and Days 1 : 2
by combining, we get,
4 × 1 × x = 3 × 2 × 8
x = 12