Final answer:
On a hot day with an ambient temperature higher than ISA and a pressure altitude at 20,000 ft, the density altitude would be higher than 20,000 ft.
Step-by-step explanation:
On a very hot day when the ambient temperature is higher than the International Standard Atmosphere (ISA), and the pressure altitude is given as 20,000 ft, the density altitude would be greater than 20,000 ft. Density altitude is the altitude relative to the standard atmosphere conditions (ISA) at which the air density would be equal to the current air density. Since hot air is less dense than cooler air, the air on a hot day at 20,000 ft would be less dense than the air at 20,000 ft under ISA conditions. Thus, you would have to ascend to a higher altitude in ISA conditions to find the equivalent less dense air, meaning the density altitude is higher on hot days.