Final answer:
The pressure in the airplane at an elevation of 12,000 feet in Lhasa, Tibet is equal to 0.634 atm.
Step-by-step explanation:
To convert the pressure from inches of mercury (in Hg) to atmospheres (atm), we can use the conversion factor of 1 atm = 29.92 in Hg.
Given that the altimeter reading in the airplane is 19.00 in Hg, we can calculate the pressure in atm as follows:
Pressure (atm) = 19.00 in Hg / 29.92 in Hg/atm = 0.634 at)
Therefore, the pressure in the airplane is equal to 0.634 atm.