About____ percent of the body weight of a human adult is contributed by muscles.

Answer

To determine the percentage of body weight contributed by muscles in a human adult, follow these steps:

1. **Identify the Average Muscle Mass**:
- For a normal human adult male, the muscle mass is approximately 30 kilograms.

2. **Understand Total Body Weight**:
- The total body weight of an average adult male is typically around 70 kilograms (this can vary based on height and body composition).

3. **Calculate the Muscle Mass Percentage**:
- To find the percentage of body weight that is muscle, use the formula:
\[ \text{Muscle Mass Percentage} = \left( \frac{\text{Muscle Mass}}{\text{Total Body Weight}} \right) \times 100 \]
- Substituting the values:
\[ \text{Muscle Mass Percentage} = \left( \frac{30 \text{ kg}}{70 \text{ kg}} \right) \times 100 \approx 42.86\% \]

4. **Consider Variability in Muscle Mass**:
- Note that muscle mass percentage varies between individuals. For men, it typically lies between 38% and 54%, while for women, it ranges from 28% to 39%.

5. **Conclude the Answer**:
- Therefore, the answer to the question is that about **38% to 54%** of the body weight of a human adult male is contributed by muscles, and for females, it is about **28% to 39%**.