29. Explain, in your own words, why in the Addition Rule for P(A or B or C), P(A and B and C) is added at the end of the formula.
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 53m
- 8. Sampling Distributions & Confidence Intervals: Proportion1h 12m
- 9. Hypothesis Testing for One Sample2h 19m
- 10. Hypothesis Testing for Two Samples3h 22m
- 11. Correlation1h 6m
- 12. Regression1h 4m
- 13. Chi-Square Tests & Goodness of Fit1h 20m
- 14. ANOVA1h 0m
4. Probability
Addition Rule
Problem 3.RE.34
Textbook Question
In Exercises 33 and 34, use the pie chart at the left, which shows the percent distribution of the number of students in U.S. public schools in a recent year. (Source: U.S. National Center for Education Statistics)

34. Find the probability of randomly selecting a school with 300 or more students.

1
Identify the relevant categories in the pie chart that represent schools with 300 or more students. These categories are '300–499', '500–999', and '1000 or more'.
Determine the percentage of students in each of these categories from the pie chart: '300–499' is 28.1%, '500–999' is 32.7%, and '1000 or more' is 9.4%.
Add these percentages together to find the total percentage of students in schools with 300 or more students. Use the formula: Total Percentage = Percentage(300–499) + Percentage(500–999) + Percentage(1000 or more).
Convert the total percentage into a probability. Since percentages are out of 100, divide the total percentage by 100 to express it as a probability.
Interpret the result as the probability of randomly selecting a school with 300 or more students.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Probability
Probability is a measure of the likelihood that a particular event will occur, expressed as a number between 0 and 1. In this context, it refers to the chance of randomly selecting a school with 300 or more students from the total distribution shown in the pie chart.
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Pie Chart Interpretation
A pie chart visually represents data as slices of a circle, where each slice corresponds to a category's proportion of the whole. Understanding how to read the percentages in the pie chart is essential for determining the probability of selecting a school based on its student population.
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Cumulative Distribution
Cumulative distribution refers to the total percentage of observations that fall below a certain value. To find the probability of selecting a school with 300 or more students, one must calculate the cumulative percentage of schools with fewer than 300 students and subtract it from 100%.
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