1. The problem statement, all variables and given/known data A 185 m3 room must be filled with 4 ppm NO2 gas (Nitrogen dioxide). The gas comes in cylinder of 200 bar and 50 liters (20x50 = 10,000 liters) and 50 ppm. How many cylinders are needed? 2. Relevant equations 1 ppm = 1/1,000,000 (parts per million) (can't think of more relevant equations) 3. The attempt at a solution To be honest I do not know how to begin. The ppm part is completely new to me.