Social Security Numbers A Social Security number consists of nine digits in a particular order, and repetition of digits is allowed. After seeing the last four digits printed on a receipt, if you randomly select the other digits, what is the probability of getting the correct Social Security number of the person who was given the receipt?
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 4.4.18
Textbook Question
Teed Off When four golfers are about to begin a game, they often toss a tee to randomly select the order in which they tee off. What is the probability that they tee off in alphabetical order by last name?

1
Step 1: Understand the problem. The goal is to calculate the probability that four golfers tee off in alphabetical order by last name. This involves determining the total number of possible orders and identifying the specific order that matches the alphabetical arrangement.
Step 2: Calculate the total number of possible orders. Since there are four golfers, the number of ways they can be arranged is given by the factorial of 4, denoted as 4!. The formula for factorial is n! = n × (n-1) × (n-2) × ... × 1. For 4 golfers, this would be 4 × 3 × 2 × 1.
Step 3: Identify the favorable outcome. There is only one specific arrangement where the golfers tee off in alphabetical order by last name. This is the favorable outcome.
Step 4: Calculate the probability. The probability of an event is given by the formula P(Event) = (Number of favorable outcomes) / (Total number of possible outcomes). Substitute the values: the number of favorable outcomes is 1, and the total number of possible outcomes is 4!.
Step 5: Simplify the expression. To find the probability, simplify the fraction using the value of 4! calculated earlier. This will give the final probability that the golfers tee off in alphabetical order by last name.

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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 quantifies the chance of the golfers teeing off in a specific order, which can be calculated by considering all possible arrangements of the golfers.
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Permutations
Permutations refer to the different ways in which a set of items can be arranged in order. For four golfers, the total number of permutations is calculated as 4! (4 factorial), which equals 24. This concept is essential for determining the total possible outcomes when arranging the golfers.
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Favorable Outcomes
Favorable outcomes are the specific outcomes that satisfy the condition of interest—in this case, the golfers teeing off in alphabetical order. Since there is only one specific arrangement that meets this criterion among the total permutations, understanding favorable outcomes is crucial for calculating the probability.
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