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
3. Describing Data Numerically
Standard Deviation
Problem 3.q.6
Textbook Question
Roller Coaster z Score A larger sample of 92 roller coaster maximum speeds has a mean of 85.9 km/h and a standard deviation of 28.7 km/h. What is the z score for a speed of 34 km/h? Does the z score suggest that the speed of 34 km/h is significantly low?

1
Step 1: Recall the formula for calculating a z-score: , where is the observed value, is the mean, and is the standard deviation.
Step 2: Identify the given values from the problem: , , and .
Step 3: Substitute the given values into the z-score formula: .
Step 4: Simplify the numerator by subtracting the mean from the observed value: . Then divide the result by the standard deviation to compute the z-score.
Step 5: Interpret the z-score. If the z-score is less than -2, it suggests that the speed of 34 km/h is significantly low compared to the mean. Otherwise, it is not considered significantly low.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Z Score
A z score, or standard score, indicates how many standard deviations an element is from the mean of a dataset. It is calculated using the formula: z = (X - μ) / σ, where X is the value in question, μ is the mean, and σ is the standard deviation. A z score can help determine the relative position of a value within a distribution, allowing for comparisons across different datasets.
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Mean and Standard Deviation
The mean is the average of a set of values, calculated by summing all values and dividing by the number of values. The standard deviation measures the amount of variation or dispersion in a set of values; a low standard deviation indicates that values tend to be close to the mean, while a high standard deviation indicates a wider spread. Together, these statistics provide a summary of the data's central tendency and variability.
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Significance in Statistics
In statistics, significance often refers to whether a result is likely due to chance or if it reflects a true effect. A z score can help assess significance by indicating how extreme a value is within a distribution. Typically, a z score beyond ±1.96 is considered significant at the 0.05 level, suggesting that the observed value is unlikely to occur under the null hypothesis, thus indicating a potential anomaly or noteworthy observation.
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