Pipe $A$ fills a tank in $8$ hr; pipe $B$ in $12$ hr; outlet $C$ empties in $24$ hr. With all open, the tank…

Pipe $A$ fills a tank in $8$ hr; pipe $B$ in $12$ hr; outlet $C$ empties in $24$ hr. With all open, the tank fills in:
  1. $5$ hr
  2. $6$ hr
  3. $7$ hr
  4. $8$ hr

Solution

Net rate $= \dfrac{1}{8} + \dfrac{1}{12} - \dfrac{1}{24} = \dfrac{3 + 2 - 1}{24} = \dfrac{4}{24} = \dfrac{1}{6}$. Time $= 6$ hr.

Asked in: IMO

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