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Ch. 5 - Discrete Probability Distributions
Triola - Elementary Statistics 14th Edition
Triola14th EditionElementary StatisticsISBN: 9780137366446Not the one you use?Change textbook
Chapter 5, Problem 5.1.2

Discrete or Continuous? Is the random variable given in the table from Exercise 1 discrete or continuous? Explain.

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Understand the definitions: A discrete random variable takes on a countable number of distinct values (e.g., integers, finite or countably infinite), while a continuous random variable can take on any value within a given range or interval (e.g., real numbers).
Examine the random variable provided in Exercise 1. Determine whether the values it can take are countable (e.g., 0, 1, 2, ...) or if they can take on any value within a range (e.g., 1.5, 2.3, etc.).
If the random variable represents something like the number of occurrences of an event (e.g., number of cars, number of students), it is likely discrete. If it represents measurements (e.g., height, weight, time), it is likely continuous.
Check whether the random variable is described in terms of intervals or specific points. Discrete variables are often associated with specific points, while continuous variables are associated with ranges or intervals.
Based on the analysis, classify the random variable as either discrete or continuous and provide a brief explanation of why it fits that classification.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Discrete Random Variables

Discrete random variables are those that can take on a countable number of distinct values. Examples include the number of students in a classroom or the outcome of rolling a die. These variables often arise in situations where the data can be enumerated, and they typically involve whole numbers.
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Continuous Random Variables

Continuous random variables, in contrast, can take on an infinite number of values within a given range. They are often associated with measurements, such as height, weight, or temperature. These variables can be represented on a number line and can include fractions and decimals, making them uncountable.
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Identifying Random Variables

To determine whether a random variable is discrete or continuous, one must analyze the nature of the data it represents. If the values can be listed or counted, it is discrete; if the values can vary continuously and include fractions, it is continuous. This distinction is crucial for selecting appropriate statistical methods for analysis.
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Related Practice
Textbook Question

If we sample from a small finite population without replacement, the binomial distribution should not be used because the events are not independent. If sampling is done without replacement and the outcomes belong to one of two types, we can use the hypergeometric distribution. If a population has A objects of one type (such as lottery numbers you selected), while the remaining B objects are of the other type (such as lottery numbers you didn’t select), and if n objects are sampled without replacement (such as six drawn lottery numbers), then the probability of getting x objects of type A and objects of type B is

In New Jersey’s Pick 6 lottery game, a bettor selects six numbers from 1 to 49 (without repetition), and a winning six-number combination is later randomly selected. Find the probability of getting exactly four winning numbers with one ticket.

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Textbook Question

Notation Assume that we want to find the probability that when five speaking characters in movies are randomly selected, exactly two of them are females. Also assume that when randomly selecting a speaking character in a movie, the probability of getting a female is 0.331. Identify the values of n, x, p, and q.

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Textbook Question

Independent Events Again assume that when randomly selecting a speaking character in a movie, the probability of getting a female is 0.331, as in Exercise 1. If we want to find the probability of 20 females when 50 different speaking characters are randomly selected from a population of 1500 speaking characters, are the 50 selections independent? Using the 5% guideline for cumbersome calculations, can they be treated as being independent?

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Textbook Question

Biometric Security In a USA Today survey of 510 people, 270 (or 53%) said that we should replace passwords with biometric security, such as fingerprints. Use the following probabilities related to determining whether the result of 270 is significantly high (assuming the true rate is 50%). Is 270 significantly high? What should be concluded about the claim that the majority of the population says that we should replace passwords with biometric security? Explain.


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Textbook Question

Lottery. In Exercises 15–20, refer to the accompanying table, which describes probabilities for the California Daily 4 lottery. The player selects four digits with repetition allowed, and the random variable x is the number of digits that match those in the same order that they are drawn (for a “straight” bet).



Range Rule of Thumb for Significant Events Use the range rule of thumb to determine whether 4 matches is a significantly high number of matches.

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Textbook Question

40% of consumers believe that cash will be obsolete in the next 20 years (based on a survey by J.P. Morgan Chase). In each of Exercises 15–20, assume that 8 consumers are randomly selected. Find the indicated probability.


Find the probability that no more than 3 of the selected consumers believe that cash will be obsolete in the next 20 years.

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