RRB Paramedical Staff Nurse Model Paper 3

Given, time taken by first tap to fill the cistern = 3 h
Thus, part of cistern filed by first tap in $1\mathit{h}=\frac{1}{3}$.... (i)
(if a pipe fills a tank in x h then the part of tank filled in $1\mathit{h}=\frac{1}{\mathit{x}}$)
Similarly, part of cistern filledby second tap in $1\mathit{h}=\frac{1}{4}$....(ii)
And part of cistern emptied by third tap in $1\mathit{h}=\frac{1}{5}$.... (iii)
Now, part of cistem filled by all taps in 1h
From above equations,
$\Rightarrow \left(\mathit{A}+\mathit{B}-\mathit{C}\right)=\frac{1}{3}+\frac{1}{4}-\frac{1}{5}$
$=\frac{20+15-12}{60}$
Hence, all three taps can fill the cistern in $\frac{60}{23}$ or $2\frac{14}{23}\mathit{h}$
(if a pipe fills $\frac{1}{\mathit{x}}$ part of the tank in 1h then the time taken by the pipe to fill the full tank $=\mathit{x}\mathit{h}$ )