# How big are your lungs?

Geometry Level 4

Both of our lungs are covered by thin membranes called pleura. The surface area of such overlying layer is about 1,000 $$\text{ cm}^{2}$$ per each lung.

Nevertheless, deep inside, the lungs contain numerous grape-like clusters of microscopic spherical sub-units, called alveoli, where the gas exchange takes place, and each alveolus has a diameter of about 200 microns. (1 micron = $$10^{-6}$$ meter)

If there are averagely 600 million alveoli in normal adult lungs, approximately, how many times is the lungs' internal surface area larger than the external one? (Round the answer to the nearest hundreds.)

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