The wavelength is related to the frequency by the relationship:

where v is the wave speed and f is its frequency.
The speed of sound in air is v=344 m/s. The lowest frequency is f=20.0 Hz, so the corresponding wavelength is

The highest frequency is

, so the corresponding wavelength is

Therefore, the range of wavelengths of audible sound in air is
[0.017 m - 17.2 m]