Assume the random variable X is normally distributed, with mean p= 44 and standard deviation o = 9. Find the 13th percentile.

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**Understanding Percentiles in a Normal Distribution**

Consider the random variable \( X \), which is normally distributed with a mean (\( \mu \)) of 44 and a standard deviation (\( \sigma \)) of 9. Our goal is to find the 13th percentile of this distribution.

### Key Concepts:

- **Normal Distribution**: A probability distribution that is symmetric about the mean, depicting that data near the mean are more frequent in occurrence than data far from the mean.
- **Mean (\( \mu \))**: The average or central value.
- **Standard Deviation (\( \sigma \))**: A measure of the amount of variation or dispersion in a set of values.
- **Percentile**: A measure used in statistics to indicate the value below which a given percentage of observations in a group falls.

### Problem Statement:

Assume the random variable \( X \) is normally distributed, with mean \( \mu = 44 \) and standard deviation \( \sigma = 9 \). Find the 13th percentile.

### Calculate the 13th Percentile:

The 13th percentile means that 13% of the data falls below this value. To find this value, you can use statistical tables or software that provides the cumulative distribution function (CDF) of the normal distribution.

1. **Z-Score Approach:** 
   - A Z-score is a measure of how many standard deviations an element is from the mean.
   - Use the standard normal distribution table to find the Z-score corresponding to a cumulative probability of 0.13.
   - Convert the Z-score to the corresponding \( X \) value using the formula: 
     \[
     X = \mu + Z \times \sigma
     \]

2. **Using Statistical Software or Tools:**
   - Input the mean, standard deviation, and desired percentile to obtain the result directly.

By following such methods, you can determine the precise value at the 13th percentile for the given normal distribution.
Transcribed Image Text:**Understanding Percentiles in a Normal Distribution** Consider the random variable \( X \), which is normally distributed with a mean (\( \mu \)) of 44 and a standard deviation (\( \sigma \)) of 9. Our goal is to find the 13th percentile of this distribution. ### Key Concepts: - **Normal Distribution**: A probability distribution that is symmetric about the mean, depicting that data near the mean are more frequent in occurrence than data far from the mean. - **Mean (\( \mu \))**: The average or central value. - **Standard Deviation (\( \sigma \))**: A measure of the amount of variation or dispersion in a set of values. - **Percentile**: A measure used in statistics to indicate the value below which a given percentage of observations in a group falls. ### Problem Statement: Assume the random variable \( X \) is normally distributed, with mean \( \mu = 44 \) and standard deviation \( \sigma = 9 \). Find the 13th percentile. ### Calculate the 13th Percentile: The 13th percentile means that 13% of the data falls below this value. To find this value, you can use statistical tables or software that provides the cumulative distribution function (CDF) of the normal distribution. 1. **Z-Score Approach:** - A Z-score is a measure of how many standard deviations an element is from the mean. - Use the standard normal distribution table to find the Z-score corresponding to a cumulative probability of 0.13. - Convert the Z-score to the corresponding \( X \) value using the formula: \[ X = \mu + Z \times \sigma \] 2. **Using Statistical Software or Tools:** - Input the mean, standard deviation, and desired percentile to obtain the result directly. By following such methods, you can determine the precise value at the 13th percentile for the given normal distribution.
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