**Core Concept**
The concept of total prevalence (also known as combined prevalence) of multiple conditions in a population involves understanding the principles of epidemiology, specifically how to calculate the total prevalence of two or more conditions when they co-occur. In this context, we need to apply the principles of probability and set theory to determine the total prevalence.

**Why the Correct Answer is Right**
To find the total prevalence of deafness and blindness together, we need to recognize that the co-occurrence of both conditions is a subset of the total population. The correct formula to calculate the total prevalence is the sum of the individual prevalences minus the product of the individual prevalences (to avoid double-counting the overlap). This is based on the principle of inclusion-exclusion in set theory. In mathematical terms, the total prevalence (P) is given by: P = P(deafness) + P(blindness) - P(deafness ∩ blindness).

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it simply adds the two individual prevalences without considering the overlap between the two conditions. This would result in an overestimation of the total prevalence.
**Option B:** This option is incorrect because it subtracts the product of the two individual prevalences without first adding the individual prevalences. This would result in an underestimation of the total prevalence.
**Option C:** This option is incorrect because it is a simple arithmetic mean of the two individual prevalences, which does not account for the overlap between the two conditions.

**Clinical Pearl / High-Yield Fact**
When calculating the total prevalence of two or more conditions, remember to use the principle of inclusion-exclusion to avoid double-counting the overlap between the conditions.

**Correct Answer:**
Correct Answer: .006