18. The weight of a full-term newborn baby follows a normal distribution with a mean weight of 7.5 pounds and a standard deviation of 1.8 pounds. Find the probability that the mean weight of a sample of 20 full-term newborn babies is less than 8.6 pounds. SHOW WORK and round your answer to 4-decimal places or answer as a precent with 1-digit value.

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18.
**Question 18:**

The weight of a full-term newborn baby follows a normal distribution with a mean weight of 7.5 pounds and a standard deviation of 1.8 pounds. Find the probability that the mean weight of a sample of 20 full-term newborn babies is less than 8.6 pounds. **SHOW WORK** and round your answer to 4-decimal places or answer as a percent with a 1-digit value.

---

**Solution Explanation:**

1. **Identify the Parameters:**
   - Population mean (\(\mu\)) = 7.5 pounds
   - Population standard deviation (\(\sigma\)) = 1.8 pounds
   - Sample size (\(n\)) = 20

2. **Calculate the Standard Error (SE):**
   \[
   SE = \frac{\sigma}{\sqrt{n}} = \frac{1.8}{\sqrt{20}}
   \]

3. **Find the Z-score:**
   - We want the probability that the sample mean is less than 8.6 pounds.
   - Compute the Z-score using:
     \[
     Z = \frac{\bar{X} - \mu}{SE} = \frac{8.6 - 7.5}{SE}
     \]

4. **Use the Z-table:**
   - Look up the computed Z-score in the standard normal distribution table to find the probability.

5. **Answer:**
   - Provide the probability to 4-decimal places or as a percentage rounded to 1-digit.
Transcribed Image Text:**Question 18:** The weight of a full-term newborn baby follows a normal distribution with a mean weight of 7.5 pounds and a standard deviation of 1.8 pounds. Find the probability that the mean weight of a sample of 20 full-term newborn babies is less than 8.6 pounds. **SHOW WORK** and round your answer to 4-decimal places or answer as a percent with a 1-digit value. --- **Solution Explanation:** 1. **Identify the Parameters:** - Population mean (\(\mu\)) = 7.5 pounds - Population standard deviation (\(\sigma\)) = 1.8 pounds - Sample size (\(n\)) = 20 2. **Calculate the Standard Error (SE):** \[ SE = \frac{\sigma}{\sqrt{n}} = \frac{1.8}{\sqrt{20}} \] 3. **Find the Z-score:** - We want the probability that the sample mean is less than 8.6 pounds. - Compute the Z-score using: \[ Z = \frac{\bar{X} - \mu}{SE} = \frac{8.6 - 7.5}{SE} \] 4. **Use the Z-table:** - Look up the computed Z-score in the standard normal distribution table to find the probability. 5. **Answer:** - Provide the probability to 4-decimal places or as a percentage rounded to 1-digit.
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