Question

Two pipes A and B can fill a cistern in 20 and 60 minutes respectively. The pipe B is opened first; after how many minutes the pipe A must also be opened so that the cistern may be filled in 10 more minutes?​

Answer 1

$\underline{\underline{\maltese\: \: \textbf{\textsf{Answer}}}}$

Let the second pipe be closed after x minutes.

$\sf{Then, \frac{10}{20} + \frac{x}{60} =1}$

$\sf{⟹ \frac{30 + x}{60}=1}$

$\sf⟹x = 60 - 30$

$\sf⟹x=30 \: min$