RRB Paramedical Staff Nurse Model Paper 4

Part of the tank
Filled by Ist = 20 min
Filled by IInd = 30 min
Then, part of the tank filled in 1h by both the pipes
$=\frac{1}{20}+\frac{1}{30}$
$=\frac{3+2}{60}=\frac{1}{12}$
Thus, required time $=12$ min
Alternate Method
Here, $\mathit{x}=20$ and $\mathit{y}=30$ Time taken by both the pipes
$=\frac{\mathit{x}\mathit{y}}{\mathit{x}+\mathit{y}}$
$=\frac{20\times 30}{20+30}$
$=\frac{600}{50}=12\mathit{m}\mathit{i}\mathit{n}$