Madhya Pradesh Police Exam Model Paper 7

Given:
Three pipes X, Y, Z can fill an overhead pot in 4, 6 and 12 hours respectively
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 all three pipes in an hours
$\Rightarrow \frac{1}{4}+\frac{1}{6}+\frac{1}{12}=\frac{6+4+2}{24}=\frac{1}{2}$
∴ The pot will be filled in 2 hours.