1. The problem statement, all variables and given/known data Given a house(with ventilation system) contains 50m3 of gases, what is minimum rate should I pump gases into the box so that the box contains completely new gas from outside in an hour? (Challenge question) 2. Relevant equations rate = volume/time statistical mechanics fluid dynamics 3. The attempt at a solution 50m3/60min = 5/6 m3/min? I do not believe the question being that simple I think some old gases will remain inside. Also, should the the answer be 10/6 m3/min (the double)?