A cistern is filled by a pipe in $4$ hr but emptied by another in $5$ hr. Both opened together, the time to fill the cistern is:

Question

Aicharya · Accepted Answer

Net rate $= \dfrac{1}{4} - \dfrac{1}{5} = \dfrac{5 - 4}{20} = \dfrac{1}{20}$. Time $= 20$ hr.

A cistern is filled by a pipe in $4$ hr but emptied by another in $5$ hr. Both opened together, the time to…