Table of contents
- 1. Intro to Stats and Collecting Data55m
- 2. Describing Data with Tables and Graphs1h 55m
- 3. Describing Data Numerically1h 45m
- 4. Probability2h 16m
- 5. Binomial Distribution & Discrete Random Variables2h 33m
- 6. Normal Distribution and Continuous Random Variables1h 38m
- 7. Sampling Distributions & Confidence Intervals: Mean1h 3m
- 8. Sampling Distributions & Confidence Intervals: Proportion1h 12m
- 9. Hypothesis Testing for One Sample1h 1m
- 10. Hypothesis Testing for Two Samples2h 8m
- 11. Correlation48m
- 12. Regression1h 4m
- 13. Chi-Square Tests & Goodness of Fit1h 20m
- 14. ANOVA1h 0m
6. Normal Distribution and Continuous Random Variables
Standard Normal Distribution
Problem 14.CRE.7a
Textbook Question
Heights On the basis of Data Set 1 “Body Data” in Appendix B, assume that heights of men are normally distributed, with a mean of 68.6 in. and a standard deviation of 2.8 in.
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a. The U.S. Coast Guard requires that men must have a height between 60 in. and 80 in. Find the percentage of men who satisfy that height requirement.

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Step 1: Understand the problem. The heights of men are normally distributed with a mean (μ) of 68.6 inches and a standard deviation (σ) of 2.8 inches. We need to find the percentage of men whose heights fall between 60 inches and 80 inches.
Step 2: Convert the given height limits (60 inches and 80 inches) into z-scores using the formula: , where x is the height, μ is the mean, and σ is the standard deviation.
Step 3: Calculate the z-score for the lower limit (60 inches) using the formula: . Similarly, calculate the z-score for the upper limit (80 inches) using the formula: .
Step 4: Use a standard normal distribution table (or a statistical software/tool) to find the cumulative probabilities corresponding to the calculated z-scores. The cumulative probability for the lower z-score gives the proportion of men shorter than 60 inches, and the cumulative probability for the upper z-score gives the proportion of men shorter than 80 inches.
Step 5: Subtract the cumulative probability of the lower z-score from the cumulative probability of the upper z-score to find the percentage of men whose heights fall between 60 inches and 80 inches. Multiply the result by 100 to express it as a percentage.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Normal Distribution
Normal distribution is a probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean. It is characterized by its bell-shaped curve, defined by its mean and standard deviation. In this context, the heights of men are assumed to follow a normal distribution, which allows for the calculation of probabilities related to height.
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Z-Scores
A Z-score is a statistical measurement that describes a value's relationship to the mean of a group of values. It is calculated by subtracting the mean from the value and then dividing by the standard deviation. Z-scores are essential for determining the percentage of a normally distributed variable that falls within a certain range, such as the height requirements set by the U.S. Coast Guard.
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Empirical Rule
The Empirical Rule, also known as the 68-95-99.7 rule, states that for a normal distribution, approximately 68% of the data falls within one standard deviation of the mean, 95% within two standard deviations, and 99.7% within three standard deviations. This rule helps in estimating the percentage of men whose heights fall within the specified range of 60 in. to 80 in., facilitating the analysis of the height requirement.
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