Hypothetical time. Say, there is a filter which picks out stuff you don't want with 70% probability. Another, filters the stuff out with 99.9% probability. Every minute, the first lets 1000 cubic meters of air pass through, the second lets 200 cubic meters of air pass through 17/

So, every minute, the first guy delivers 1000 cubic feet air, 70% likely to be clean. So that is about 700 cubic feet clean air every minute. The second guy delivers 199.8 cubic feet clean air every minute. 18/