Aptitude Discussion

Q. |
Pipes $A$ and $B$ can fill a tank in 12 min and 16 min respectively. Both are kept open for '$n$' min and then $B$ is closed and $A$ fills the rest of the tank in 5 min. The time '$n$' after which $B$ was closed is: |

✖ A. |
3 min |

✖ B. |
2 min |

✖ C. |
5 min |

✔ D. |
4 min |

**Solution:**

Option(**D**) is correct

\(n\left(\dfrac{1}{12}+\dfrac{1}{16}\right)=\dfrac{28n}{192}\)

$\Rightarrow$ Left capacity = \(1-\dfrac{28n}{192}\)

This is filled by $A$ in 5 min and fills \(\dfrac{1}{12}\) in 1 min

\(\Rightarrow \dfrac{192-28x}{192}=\dfrac{5}{12}\)

$n$= **4 min**

**Vaibhav Gupta**

*()
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Alternative:

Clearly,

n+5/12+n/16=1

Solving it we get n=4