Time and Work
Aptitude

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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

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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


(1) Comment(s)


Vaibhav Gupta
 ()

Alternative:

Clearly,

n+5/12+n/16=1

Solving it we get n=4