A normal subject is breathing room air and expiring into a large collection bag. When the expired air is analyzed, the mean expired PECO2 is measured at 30 mm Hg. When the arterial blood is sampled, PaCO2 is measured at 50 mm Hg. The subject’s respiratory frequency is 15 breaths per minute and her average tidal volume is 500 ml. 1. Calculate the physiological dead space fraction. 2. Calculate the alveolar ventilation. 3. Calculate the CO2 production rate.