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Asurvey involving 400 likely Democratic voters and 300 likely Republican voters asked the question: Do you support or oppose legislation that would require registration of all handguns? The following results were obtained: $$\begin{array}{lcc} \hline \text { Answer } & \text { Democrats, \% } & \text { Republicans, \% } \\\ \hline \text { Support } & 77 & 59 \\ \hline \text { Oppose } & 14 & 31 \\ \hline \text { Don't know/refused } & 9 & 10 \\ \hline \end{array}$$ If a randomly chosen respondent in the survey answered "oppose," what is the probability that he or she is a likely Democratic voter?

Short Answer

Expert verified
The probability that a randomly chosen respondent in the survey who answered "oppose" is a likely Democratic voter is approximately \(0.198\) or \(19.8\%\).

Step by step solution

01

Identify the given information

From the exercise, we are given: - Total Democratic voters: 400 - Total Republican voters: 300 - Percentage of Democratic voters who oppose: 14% - Percentage of Republican voters who oppose: 31% - Total respondents: 700 (400 Democratic + 300 Republican)
02

Calculate probabilities

We need to find the probability of randomly selecting an individual who opposes the legislation and is a likely Democratic voter. Let A be the event of being a Democratic voter, and B be the event of opposing the legislation. We have the following probabilities: - P(A) = Probability of being a Democratic voter - P(B|A) = Probability of opposing the legislation given they are a Democratic voter - P(B|A') = Probability of opposing the legislation given they are not a Democratic voter (i.e., they are a Republican voter) Calculating these probabilities: - P(A) = Number of Democratic voters / Total respondents = 400 / 700 - P(B|A) = Percentage of Democratic voters who oppose = 14% - P(B|A') = Percentage of Republican voters who oppose = 31% We now need to find the conditional probability P(A|B), which is the probability of being a Democratic voter, given that the individual opposes the legislation.
03

Apply Bayes' theorem

Bayes' theorem states that: P(A|B) = P(B|A) * P(A) / (P(B|A) * P(A) + P(B|A') * P(A')) Replacing the known probabilities: P(A|B) = (0.14 * (400/700)) / ((0.14 * (400/700)) + (0.31 * (300/700)))
04

Solve for P(A|B)

P(A|B) = (0.14 * (400/700)) / ((0.14 * (400/700)) + (0.31 * (300/700))) = 0.198198
05

Interpret the result

The probability that a randomly chosen respondent in the survey who answered "oppose" is a likely Democratic voter is approximately 0.198 or 19.8%.

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Key Concepts

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

Bayes' theorem
Bayes' theorem is a fundamental concept in probability theory, playing a critical role in various fields, from statistics to machine learning. It provides a way to update our belief about the likelihood of a hypothesis (such as being a Democrat or Republican in the context of the survey) based on new evidence (like their stance on legislation).

In essence, Bayes' theorem helps us calculate the probability of an event, given that another event has occurred, which is known as the conditional probability. The formula for Bayes' theorem is given by: \[ P(A|B) = \frac{P(B|A)P(A)}{P(B)} \] where:
  • \( P(A|B) \) is the probability of event A occurring given that B has occurred.
  • \( P(B|A) \) is the probability of event B occurring given that A has occurred.
  • \( P(A) \) is the probability of event A occurring.
  • \( P(B) \) is the probability of event B occurring.
In the exercise, the use of Bayes' theorem allowed the determination of the likelihood that a randomly selected individual who opposes handgun registration is a likely Democratic voter, revealing the interconnected probabilities at play between political affiliation and policy stance.
Probability theory
Probability theory is the branch of mathematics that deals with the analysis of random events. The fundamental aspect of probability is to measure the likelihood of the occurrence of an event. Events can range from simple situations like flipping a coin to complex scenarios like predicting weather patterns or stock market fluctuations.

The theory uses mathematical axioms to derive other event probabilities, such as conditional probability, which is the probability of an event occurring, given that another event has already occurred. In the survey problem, probability theory is applied when we calculate the percentage of respondents from each political party that oppose handgun legislation and how these percentages translate into overall chances when randomly picking someone from the survey pool.

Moreover, probability theory supports the logic behind decision-making processes, helping us to understand and quantify uncertainty. By applying principles such as Bayes' theorem, individuals and organizations can make more informed decisions, taking into account the likelihood and impact of different outcomes based on the data available.
Finite mathematics
Finite mathematics is an area that includes various mathematical subjects applied in business, economics, life sciences, and social sciences. It incorporates topics such as algebra, graph theory, mathematical modeling, and optimization. Despite its name, finite mathematics also covers aspects of infinite processes when it comes to topics such as sequences and series.

Conditional probability and Bayes' theorem, which are parts of probability theory, are also a significant part of finite mathematics since they involve calculations that are finite in nature. Finite mathematics prepares students to think logically and to understand the quantifiable aspects of complex real-world problems.

In the context of the survey problem involving Democratic and Republican voters, finite mathematics emphasizes the practical application of mathematical theories. It breaks down complicated scenarios into finite, manageable parts — in this case, into numbers of voters and percentages — that can be analyzed individually to reach a comprehensive, quantitatively-driven conclusion.

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Most popular questions from this chapter

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