56. Defective Disks A pack of 100 recordable DVDs contains 5 defective disks. You select four disks. What is the probability of selecting at least three non defective disks?
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
Counting
Problem 3.R.46
Textbook Question
In Exercises 45-48, use combinations and permutations.
46. Five players on a basketball team must each choose one of the five players on the opposing team to defend. In how many ways can the players choose their defensive assignments?

1
Step 1: Recognize that this is a permutations problem because the order in which the defensive assignments are made matters. Each player on the basketball team is assigned to defend a specific player on the opposing team.
Step 2: Recall the formula for permutations, which is used when the order of selection matters. The formula is P(n, r) = n! / (n - r)!, where n is the total number of items to choose from, and r is the number of items being chosen.
Step 3: In this problem, there are 5 players on the basketball team and 5 players on the opposing team. Since all 5 players are being assigned, n = 5 and r = 5. Substitute these values into the permutation formula: P(5, 5) = 5! / (5 - 5)!.
Step 4: Simplify the expression. The factorial of 5 (5!) is calculated as 5 × 4 × 3 × 2 × 1. The factorial of 0 (0!) is defined as 1. Therefore, P(5, 5) = 5! / 1.
Step 5: Conclude that the total number of ways the players can choose their defensive assignments is equal to the value of 5!. This represents the number of permutations of 5 players.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Permutations
Permutations refer to the different arrangements of a set of items where the order matters. In the context of the basketball question, each player choosing a defender from the opposing team represents a unique arrangement, as the specific choice of defender by each player affects the overall assignment.
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Introduction to Permutations
Combinations
Combinations involve selecting items from a larger set where the order does not matter. While the basketball scenario primarily deals with permutations, understanding combinations is essential for grasping how selections can be made without regard to the order of choices, which can be relevant in different contexts.
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Combinations
Factorial
Factorial, denoted as n!, is the product of all positive integers up to n. It is a fundamental concept in counting arrangements and is used to calculate the total number of ways to arrange or select items. In the basketball problem, factorials help determine the total number of unique defensive assignments based on the players' choices.
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Combinations
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