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Ch. 5 - Discrete Probability Distributions
Triola - Elementary Statistics 14th Edition
Triola14th EditionElementary StatisticsISBN: 9780137366446당신이 사용하는 게 아니라요?교과서 변경
5장, 문제 5.1.5

Identifying Discrete and Continuous Random Variables. In Exercises 5 and 6, refer to the given values, then identify which of the following is most appropriate: discrete random variable, continuous random variable, or not a random variable.






a. IQ scores of statistics students
b. Exact heights of statistics students
c. Shoe sizes (such as 8 or 8½) of statistics students
d. Majors (such as history) of statistics students
e. The number of rolls of a die required for a statistics student to get the number 4

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Step 1: Understand the definitions of discrete and continuous random variables. A discrete random variable takes on a countable number of distinct values, such as integers or specific categories. A continuous random variable can take on any value within a given range, often involving measurements like height or weight. If the variable does not involve randomness, it is not a random variable.
Step 2: Analyze part (a): IQ scores of statistics students. IQ scores are numerical values but are typically measured in whole numbers and are not continuous measurements. Determine whether this fits the definition of a discrete random variable or not.
Step 3: Analyze part (b): Exact heights of statistics students. Heights are measured on a continuous scale, meaning they can take on any value within a range (e.g., 5.5 feet, 5.55 feet). Determine whether this fits the definition of a continuous random variable.
Step 4: Analyze part (c): Shoe sizes of statistics students. Shoe sizes are typically discrete values (e.g., 8, 8½) and are countable. Determine whether this fits the definition of a discrete random variable.
Step 5: Analyze parts (d) and (e): Majors of statistics students and the number of rolls of a die required to get a 4. Majors are categorical and not numerical, so they are not random variables. The number of rolls of a die is countable and fits the definition of a discrete random variable.

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주요 개념

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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 class or the number of rolls of a die. These variables often represent counts or categories, making them suitable for statistical analysis where specific outcomes can be enumerated.
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가이드 코스
04:48
Variance & Standard Deviation of Discrete Random Variables

Continuous Random Variables

Continuous random variables can take on an infinite number of values within a given range. They are typically measurements, such as height or weight, where any value within a range is possible. This type of variable is often represented using intervals and is analyzed using techniques that account for the continuum of possible values.
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가이드 코스
07:09
Intro to Random Variables & Probability Distributions

Random Variables

A random variable is a numerical outcome of a random phenomenon, which can be classified as either discrete or continuous. It serves as a bridge between probability and statistics, allowing for the quantification of uncertainty. Understanding random variables is essential for analyzing data and making predictions based on probabilistic models.
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가이드 코스
07:09
Intro to Random Variables & Probability Distributions
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교과서 질문

Texting and Driving. In Exercises 21–26, refer to the accompanying table, which describes probabilities for groups of five drivers. The random variable x is the number of drivers in a group who say that they text while driving (based on data from an Arity survey of drivers).

Using Probabilities for Significant Events


a. Find the probability of getting exactly 3 drivers who say that they text while driving.


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교과서 질문

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 at least 6 of the selected consumers believe that cash will be obsolete in the next 20 years.

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교과서 질문

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 fewer than 3 of the selected consumers believe that cash will be obsolete in the next 20 years.

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교과서 질문

Texting and Driving. In Exercises 21–26, refer to the accompanying table, which describes probabilities for groups of five drivers. The random variable x is the number of drivers in a group who say that they text while driving (based on data from an Arity survey of drivers).

Range Rule of Thumb for Significant Events Use the range rule of thumb to determine whether 4 is a significantly high number of drivers who say that they text while driving.

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교과서 질문

Exercises 33 and 34 involve the method of composite sampling, whereby a medical testing laboratory saves time and money by combining blood samples for tests so that only one test is conducted for several people. A combined sample tests positive if at least one person has the disease. If a combined sample tests positive, then individual blood tests are used to identify the individual with the disease or disorder.


HIV It is estimated that in the United States, the proportion of people infected with the human immunodeficiency virus (HIV) is 0.00343. In tests for HIV, blood samples from 50 different people are combined. What is the probability that the combined sample tests positive for HIV? Is it unlikely for such a combined sample to test positive?

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교과서 질문

In Exercises 9–16, use the Poisson distribution to find the indicated probabilities.


Murders In a recent year (365 days), there were 650 murders in Chicago. Find the mean number of murders per day, then use that result to find the probability that in a single day, there are no murders. Would 0 murders in a single day be a significantly low number of murders?

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