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Suppose that an individual is randomly selected from the population of all adult males living in the United States. Let \(A\) be the event that the selected individual is over 6 feet in height, and let \(B\) be the event that the selected individual is a professional basketball player. Which do you think is larger, \(P(A \mid B)\) or \(P(B \mid A)\) ? Why?

Short Answer

Expert verified
The probability that an individual is over 6 feet in height given that they are a professional basketball player \(P(A \mid B)\) is likely to be larger than the probability that an individual is a professional basketball player given that they are over 6 feet in height \(P(B \mid A)\). This is based on the fact that most professional basketball players tend to be over 6 feet tall, but not all individuals over 6 feet are professional basketball players.

Step by step solution

01

Understanding Event A and B

Event A is defined as the selected individual being over 6 feet in height. Event B is defined as the selected individual being a professional basketball player.
02

Understanding Probability of A given B

The probability of A given B \(P(A \mid B)\) is interpreted as the probability that the selected individual is over 6 feet tall, given that they are a professional basketball player. Since most of the professional basketball players are over 6 feet tall, this probability will be quite high.
03

Understanding Probability of B given A

The probability of B given A \(P(B \mid A)\) is the probability that the individual is a professional basketball player given that they are over 6 feet tall. While a good number of people over 6 feet may play basketball, not all of them are professional basketball players. Therefore, even though the person is over 6 feet tall, the probability of them being a professional basketball player is relatively low.
04

Comparing Probabilities

Comparing the probabilities, we can conclude that \(P(A \mid B)\) is likely larger than \(P(B \mid A)\). This is because while most professional basketball players are likely to be over 6 feet in height, not all individuals over 6 feet are professional basketball players.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Probability Theory
Probability Theory is a branch of mathematics that deals with the study of random phenomena and uncertainty. In everyday terms, probability gives us a way to quantify how likely an event is to occur. When dealing with complex scenarios where multiple events are interacting, such as in our exercise, understanding these interactions is crucial for predictive analysis.

In Probability Theory, an event is simply a collection of outcomes from a sample space. For example, in our exercise, Event A is that a person is over 6 feet tall, and Event B is that a person is a professional basketball player. Probability measures, like \( P(A) \) or \( P(B) \), quantify the likelihood of an event occurring within that sample space.

The concept of conditional probability, like \( P(A \mid B) \), is central to understanding how the probability of an event can change when we know that another event has occurred. This is important because real-world events often don’t occur in isolation; they are influenced by other events around them.
Bayes' Theorem
Bayes' Theorem is a powerful tool in statistics used to update the probability of a hypothesis based on new evidence. It relates the conditional and marginal probabilities of events and, when applied, can solve complex probability puzzles like the one in our exercise.

The theorem states as follows:\[ P(A \mid B) = \frac{P(B \mid A) \cdot P(A)}{P(B)} \]Bayes' Theorem essentially allows us to "flip" conditional probabilities, turning \( P(B \mid A) \) into \( P(A \mid B) \) and vice versa, by taking into account known probabilities of the complementary events.

In practical terms, if we have sufficient data on the likelihood of certain conditions, Bayes' Theorem provides a framework to effectively reassess our probabilities when new or different facts are introduced into the problem.
Event Probability
Event Probability refers to the likelihood of a specific event occurring within a defined sample space. This fundamental concept is the backbone of understanding outcomes in both simple and complex situations, like the one outlined in our exercise.

When considering event probability, it’s important to identify the event in question and its defining characteristics. Event A might involve a height attribute, while Event B concerns a specific profession. Understanding the nature of these events aids in calculating their probabilities accurately.

The probabilities of complex events are often linked via conditional probabilities. They reflect how one event affects or is affected by another. In our exercise, estimating the probability of someone being a professional basketball player given their height (\( P(B \mid A) \)), or the reverse, is pivotal in determining which probability is larger. This reinforces the idea that individual probabilities can inherently relate to external conditions, offering a richer reality of how events may unfold.

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Most popular questions from this chapter

The report "Twitter in Higher Education: Usage Habits and Trends of Today's College Faculty" (Magna Publications, September 2009) describes results of a survey of nearly 2000 college faculty. The report indicates the following: \- \(30.7 \%\) reported that they use Twitter and \(69.3 \%\) said that they did not use Twitter. \- Of those who use Twitter, \(39.9 \%\) said they sometimes use Twitter to communicate with students. \- Of those who use Twitter, \(27.5 \%\) said that they sometimes use Twitter as a learning tool in the classroom. Consider the chance experiment that selects one of the study participants at random and define the following events: \(T=\) event that selected faculty member uses Twitter \(C=\) event that selected faculty member sometimes uses Twitter to communicate with students \(L=\) event that selected faculty member sometimes uses Twitter as a learning tool in the classroom a. Use the given information to determine the following probabilities: i. \(\quad P(T)\) ii. \(P\left(T^{C}\right)\) iii. \(P(C \mid T)\) iv. \(P(L \mid T)\) v. \(P(C \cap T)\) b. Interpret each of the probabilities computed in Part (a). c. What proportion of the faculty surveyed sometimes use Twitter to communicate with students? [Hint: Use the law of total probability to find \(P(C) .]\) d. What proportion of faculty surveyed sometimes use Twitter as a learning tool in the classroom?

A new model of laptop computer can be ordered with one of three screen sizes ( 10 inches, 12 inches, 15 inches) and one of four hard drive sizes \((50 \mathrm{~GB}, 100 \mathrm{~GB}\), \(150 \mathrm{~GB}\), and \(200 \mathrm{~GB}\) ). Consider the chance experiment in which a laptop order is selected and the screen size and hard drive size are recorded. a. Display possible outcomes using a tree diagram. b. Let \(A\) be the event that the order is for a laptop with a screen size of 12 inches or smaller. Let \(B\) be the event that the order is for a laptop with a hard drive size of at most \(100 \mathrm{~GB}\). What outcomes are in \(A^{C}\) ? In \(A \cup B ?\) In \(A \cap B\) ? c. Let \(C\) denote the event that the order is for a laptop with a \(200 \mathrm{~GB}\) hard drive. Are \(A\) and \(C\) disjoint events? Are \(B\) and \(C\) disjoint?

Two individuals, \(A\) and \(B\), are finalists for a chess championship. They will play a sequence of games, each of which can result in a win for \(A\), a win for \(\mathrm{B}\), or a draw. Suppose that the outcomes of successive games are independent, with \(P(\) A wins game \()=.3\), \(P(\) B wins game \()=.2\), and \(P(\) draw \()=.5\). Each time a player wins a game, he earns 1 point and his opponent earns no points. The first player to win 5 points wins the championship. For the sake of simplicity, assume that the championship will end in a draw if both players obtain 5 points at the same time. a. What is the probability that \(A\) wins the championship in just five games? b. What is the probability that it takes just five games to obtain a champion? c. If a draw earns a half-point for each player, describe how you would perform a simulation to estimate \(\mathrm{P}(\mathrm{A}\) wins the championship). d. If neither player earns any points from a draw, would the simulation in Part (c) take longer to perform? Explain your reasoning.

The events \(E\) and \(T_{j}\) are defined as \(E=\) the event that someone who is out of work and actively looking for work will find a job within the next month and \(T_{i}=\) the event that someone who is currently out of work has been out of work for \(i\) months. For example, \(T_{2}\) is the event that someone who is out of work has been out of work for 2 months. The following conditional probabilities are approximate and were read from a graph in the paper "The Probability of Finding a Job" (American Economic Review: Papers \& Proceedings [2008]: \(268-273\) ) $$ \begin{array}{ll} P\left(E \mid T_{1}\right)=.30 & P\left(E \mid T_{2}\right)=.24 \\ P\left(E \mid T_{3}\right)=.22 & P\left(E \mid T_{4}\right)=.21 \\ P\left(E \mid T_{5}\right)=.20 & P\left(E \mid T_{6}\right)=.19 \\ P\left(E \mid T_{7}\right)=.19 & P\left(E \mid T_{8}\right)=.18 \\ P\left(E \mid T_{9}\right)=.18 & P\left(E \mid T_{10}\right)=.18 \\ P\left(E \mid T_{11}\right)=.18 & P\left(E \mid T_{12}\right)=.18 \end{array} $$ a. Interpret the following two probabilities: i. \(\quad P\left(E \mid T_{1}\right)=.30\) ii. \(\quad P\left(E \mid T_{6}\right)=.19\) b. Construct a graph of \(P\left(E \mid T_{i}\right)\) versus \(i\). That is, plot \(P\left(E \mid T_{i}\right)\) on the \(y\) -axis and \(i=1,2, \ldots, 12\) on the \(x\) -axis. c. Write a few sentences about how the probability of finding a job in the next month changes as a function of length of unemployment.

After all students have left the classroom, a statistics professor notices that four copies of the text were left under desks. At the beginning of the next lecture, the professor distributes the four books at random to the four students \((1,2,3\), and 4\()\) who claim to have left books. One possible outcome is that 1 receives 2's book, 2 receives 4's book, 3 receives his or her own book, and 4 receives l's book. This outcome can be abbreviated \((2,4,3,1)\). a. List the 23 other possible outcomes. b. Which outcomes are contained in the event that exactly two of the books are returned to their correct owners? Assuming equally likely outcomes, what is the probability of this event? c. What is the probability that exactly one of the four students receives his or her own book? d. What is the probability that exactly three receive their own books? e. What is the probability that at least two of the four students receive their own books?

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