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Ch. 4 - Discrete Probability Distributions
Larson - Elementary Statistics: Picturing the World 8th Edition
Larson8th EditionElementary Statistics: Picturing the WorldISBN: 9780137493470당신이 사용하는 게 아니라요?교과서 변경
4장, 문제 4.3.26c

Using a Distribution to Find Probabilities In Exercises 11–26, find the indicated probabilities using the geometric distribution, the Poisson distribution, or the binomial distribution. Then determine whether the events are unusual. If convenient, use a table or technology to find the probabilities.


Oil Tankers In the month of June 2021, 240 oil tankers stop at a port city. No oil tanker visits more than once. Find the probability that the number of oil tankers that stop on any given day in June is (c) more than eight.

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Step 1: Identify the type of distribution to use. Since the problem involves counting the number of oil tankers stopping at a port city on a given day, and the events occur over a fixed interval (days in June), the Poisson distribution is appropriate. The Poisson distribution is used to model the number of events occurring in a fixed interval of time or space when the events occur independently and at a constant average rate.
Step 2: Calculate the average rate (λ) of oil tankers stopping per day. The total number of oil tankers in June is 240, and June has 30 days. Therefore, the average rate is λ = 240 / 30 = 8 oil tankers per day.
Step 3: Define the probability formula for the Poisson distribution. The probability of observing k events in a Poisson distribution is given by: P(X = k) = (λ^k * e^(-λ)) / k!, where λ is the average rate, k is the number of events, and e is the base of the natural logarithm (approximately 2.718).
Step 4: To find the probability that the number of oil tankers stopping on a given day is more than 8, calculate P(X > 8). This can be expressed as 1 - P(X ≤ 8). Use the cumulative probability formula to calculate P(X ≤ 8), which is the sum of probabilities for k = 0, 1, 2, ..., 8: P(X ≤ 8) = Σ [(λ^k * e^(-λ)) / k!] for k = 0 to 8.
Step 5: Use technology (e.g., a statistical calculator, software, or a Poisson distribution table) to compute P(X ≤ 8) and subtract it from 1 to find P(X > 8). Finally, compare the result to a threshold (e.g., 0.05) to determine if the event is unusual. An event is typically considered unusual if its probability is less than 0.05.

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주요 개념

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Geometric Distribution

The geometric distribution models the number of trials needed to achieve the first success in a series of independent Bernoulli trials. It is characterized by a constant probability of success on each trial. In the context of the question, it can be used to find the probability of a certain number of oil tankers stopping at the port on a given day, assuming each day is an independent trial.
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Intro to Frequency Distributions

Poisson Distribution

The Poisson distribution is used to model the number of events occurring within a fixed interval of time or space, given a known average rate of occurrence. It is particularly useful for rare events. In this scenario, it can help determine the probability of more than eight oil tankers stopping at the port on any given day in June, based on the average number of tankers per day.
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Intro to Frequency Distributions

Binomial Distribution

The binomial distribution describes the number of successes in a fixed number of independent Bernoulli trials, each with the same probability of success. It is applicable when there are two possible outcomes (success or failure) for each trial. While this distribution may not be the primary focus for the given problem, understanding it is essential for comparing it with the Poisson and geometric distributions in terms of event occurrence.
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Mean & Standard Deviation of Binomial Distribution
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교과서 질문

Finding Probabilities Use the probability distribution you made in Exercise 19 to find the probability of randomly selecting a household that has (d) at most two HD televisions.

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교과서 질문

Unusual Events In Exercises 37 and 38, find the indicated probabilities. Then determine if the event is unusual. Explain your reasoning.


Rock-Paper-Scissors The probability of winning a game of rock-paper-scissors is 1/3. You play nine games of rock-paper-scissors. Find the probability that the number of games you win is (c) less than two.

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교과서 질문

Hypergeometric Distribution Binomial experiments require that any sampling be done with replacement because each trial must be independent of the others. The hypergeometric distribution also has two outcomes: success and failure. The sampling, however, is done without replacement. For a population of N items having k successes and failures, the probability of selecting a sample of size that has successes and failures is given by

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In a shipment of 15 microchips, 2 are defective and 13 are not defective. A sample of three microchips is chosen at random. Use the above formula to find the probability that (c) two microchips are defective and one is not defective.

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교과서 질문

Finding Probabilities Use the probability distribution you made in Exercise 19 to find the probability of randomly selecting a household that has (c) from one to three HD televisions,

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