A cistern can be filled by a tap in 4 hours and emptied by an outlet in 6 hours. The cistern is one-third full when both are opened. How long until it is full?

Question

Accepted Answer

8 h. Net rate =1/4-1/6=1/12. Remaining 2/3 takes 2/3×12=8 h. (12 h fills an empty cistern.)

A cistern can be filled by a tap in 4 hours and emptied by an outlet in 6 hours. The cistern is one-third full when both are opened. How long until it is full?

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