Final answer:
A 100-Hz tone must be 2.5 times more intense than a 4000-Hz tone for an individual with certain hearing thresholds to find them equally audible.
Step-by-step explanation:
The question pertains to how different frequencies of sound are perceived by a person with varying levels of hearing threshold, specifically at 100 Hz and 4000 Hz. The individual in question would need to experience a sound at 100 Hz that is more intense compared to a sound at 4000 Hz to find them equally audible.
Considering that every 10 dB increase in sound level represents a tenfold increase in intensity, a 100-Hz tone must be 2.5 times more intense than a 4000-Hz tone for the person to barely hear them due to the raised threshold for these frequencies. This calculation assumes an average hearing threshold, where the tone at 100 Hz requires to be only slightly more intense, reflecting the particular hearing loss at higher frequencies.