The duration of gestation in healthy humans is approximately normally distributed with a mean of 280 days and a standard deviation of 10 days. A certain obstetrician has 200 "expecting" patients. How many should he expect to give birth in less than 265 days ?

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**Question 8: Understanding Normal Distribution in Human Gestation**

The duration of gestation in healthy humans is approximately normally distributed with a mean of 280 days and a standard deviation of 10 days. If an obstetrician has 200 "expecting" patients, how many should he expect to give birth in less than 265 days?

**Analysis:**

To solve this problem, we need to understand how normal distribution works. In a normal distribution:

- The mean (average) is 280 days.
- The standard deviation (a measure of how spread out numbers are) is 10 days.

We are asked to find the number of patients who are expected to give birth in less than 265 days. This requires calculating the probability of a gestation period being less than 265 days and then applying that probability to the total number of patients.

**Calculation Steps**:

1. **Determine the Z-score**: The Z-score tells us how many standard deviations a particular value is from the mean.
   
   \[
   Z = \frac{X - \mu}{\sigma}
   \]

   Where:
   - \(X\) is the value for which we are finding the Z-score (265 days).
   - \(\mu\) is the mean (280 days).
   - \(\sigma\) is the standard deviation (10 days).
   
   \[
   Z = \frac{265 - 280}{10} = \frac{-15}{10} = -1.5
   \]

2. **Find the Probability**: Using the Z-score, we can find the probability by looking up -1.5 in the standard normal distribution table, or using a calculator.

   Approximately \(P(Z < -1.5) = 0.0668\).

3. **Calculate the Expected Number of Patients**: Multiply the probability by the total number of patients.
   
   \[
   \text{Number of patients} = 0.0668 \times 200 = 13.36
   \]

   Since the number of patients cannot be a fraction, the obstetrician can expect about 13 patients to give birth in less than 265 days.
Transcribed Image Text:**Question 8: Understanding Normal Distribution in Human Gestation** The duration of gestation in healthy humans is approximately normally distributed with a mean of 280 days and a standard deviation of 10 days. If an obstetrician has 200 "expecting" patients, how many should he expect to give birth in less than 265 days? **Analysis:** To solve this problem, we need to understand how normal distribution works. In a normal distribution: - The mean (average) is 280 days. - The standard deviation (a measure of how spread out numbers are) is 10 days. We are asked to find the number of patients who are expected to give birth in less than 265 days. This requires calculating the probability of a gestation period being less than 265 days and then applying that probability to the total number of patients. **Calculation Steps**: 1. **Determine the Z-score**: The Z-score tells us how many standard deviations a particular value is from the mean. \[ Z = \frac{X - \mu}{\sigma} \] Where: - \(X\) is the value for which we are finding the Z-score (265 days). - \(\mu\) is the mean (280 days). - \(\sigma\) is the standard deviation (10 days). \[ Z = \frac{265 - 280}{10} = \frac{-15}{10} = -1.5 \] 2. **Find the Probability**: Using the Z-score, we can find the probability by looking up -1.5 in the standard normal distribution table, or using a calculator. Approximately \(P(Z < -1.5) = 0.0668\). 3. **Calculate the Expected Number of Patients**: Multiply the probability by the total number of patients. \[ \text{Number of patients} = 0.0668 \times 200 = 13.36 \] Since the number of patients cannot be a fraction, the obstetrician can expect about 13 patients to give birth in less than 265 days.
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