Average hearing at 500, 1000, 2000 Hz is 45 db in the left ear. Percentage hearing loss in left ear is, when 25 dB loss is considered normal:
**Core Concept**
The question tests the understanding of calculating percentage hearing loss based on average decibel (dB) levels at specific frequencies. **Hearing loss** is a common clinical condition, and understanding its quantification is crucial for diagnosis and management. The **decibel scale** is used to measure the intensity of sound.
**Why the Correct Answer is Right**
To calculate the percentage hearing loss, we first need to determine the average hearing threshold in the affected ear and compare it to the normal threshold. Given that 25 dB is considered normal, the excess hearing loss is 45 dB - 25 dB = 20 dB. The percentage hearing loss can then be calculated based on this excess loss, considering the maximum audible range and the dynamic range of hearing.
**Why Each Wrong Option is Incorrect**
**Option A:** This option might underestimate the hearing loss by not accurately accounting for the excess loss over the normal threshold.
**Option B:** This could overestimate or incorrectly calculate the percentage loss without considering the proper formula or reference values.
**Option C:** This might not accurately reflect the calculation method for percentage hearing loss based on the given decibel levels.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that the calculation of percentage hearing loss involves understanding the normal threshold, the patient's threshold, and applying the correct formula. The **World Health Organization (WHO)** provides guidelines on grading hearing loss, which can be crucial for clinical assessments.
**Correct Answer:** C. 40%