Madhya Pradesh Police Exam Model Paper 7

Given:
The first tap can fill it in 4 hours and the second tap can empty it in 16 hours
Concept:
If a tap can fill a tank in x hours, then the tank filled by the tap in 1 hour = 1/x of the total tank.
Calculation:
Part of the pot filled by both the taps in 1 hours $=\frac{1}{4}-\frac{1}{16}$
$\Rightarrow \frac{4-1}{16}=\frac{3}{16}$
Time $=\left(16/3\right)$ hours $=5\frac{1}{3}$ hours
∴ The required time is $5\frac{1}{3}$ hours.