If inhaled air contains21% oxygen by volume and exhaled air is 16% oxygen by volume, what is the volume of air per breath? A resting adult requires about 240mL of pure oxygen/min and breathes about 12 times every minute. (Assume that the volume of inhaled air is equal to that of exhaled air.)
240 / 12 = 20 mL of oxygen/min.
20mL = .37x (x: total vol. per breath)
x = 54.054mL
54mL - 20mL = 34mL