Chapter 12: Problem 12
In Problems \(9-12\), assume that $$ \Omega=\\{1,2,3,4,5\\} $$ \(P(1)=0.1, P(2)=0.2\), and \(P(3)=P(4)=0.05 .\) Furthermore, assume that \(A=\\{1,3,5\\}\) and \(B=\\{2,3,4\\}\). Find \(P(A \cup B)\).
Short Answer
Expert verified
The probability \(P(A \cup B) = 1.0\).
Step by step solution
01
Identify Elements in A and B
Recall the sets given: - Set \( A = \{1, 3, 5\} \) - Set \( B = \{2, 3, 4\} \). We need to find the union of these two sets, \( A \cup B \), which includes all elements that are in \( A \), \( B \), or both.
02
Find the Union A ∪ B
The union of sets \( A \) and \( B \) consists of all unique elements from both sets. Thus, we have:\[ A \cup B = \{1, 2, 3, 4, 5\} \] each element present in either \( A \) or \( B \) is included.
03
Determine the Probability of Each Element in A ∪ B
We need to list the probabilities of each element in \( A \cup B \):- \( P(1) = 0.1 \)- \( P(2) = 0.2 \)- \( P(3) = 0.05 \)- \( P(4) = 0.05 \)- We assume \( P(5) \) must be defined to complete \( \Omega \)'s total 1 probability. Since no probability is given, it can be computed as:\[ P(5) = 1 - (P(1) + P(2) + P(3) + P(4)) = 1 - (0.1 + 0.2 + 0.05 + 0.05) = 0.6 \].
04
Calculate P(A ∪ B)
We now find \( P(A \cup B) \) by summing the probabilities of all elements in the union:\[P(A \cup B) = P(1) + P(2) + P(3) + P(4) + P(5) = 0.1 + 0.2 + 0.05 + 0.05 + 0.6 = 1.0.\]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Set Theory
Set theory is a mathematical concept that deals with the collection of objects. These objects are often referred to as "elements" or "members" of the set. Let's break down some basic ideas:
- **Sets** are written with curly brackets and can contain numbers, symbols, or other sets. For example, the set containing the numbers 1, 3, and 5 would be written as \( \{1, 3, 5\} \).
- Set theory is foundational in mathematics, particularly in probability, as it provides a clear language to discuss collections of objects.
- **Equality of sets**: Two sets are equal if they contain the same elements, regardless of the order. For example, \( \{1, 3, 5\} \) is equal to \( \{5, 3, 1\} \).
- We often represent the universal set, denoted \( \Omega \), as the set of all possible outcomes. It includes every element under consideration.
Union of Sets
The union of sets is a fundamental operation in set theory, symbolized by \( \cup \). When you take the union of two sets, you combine all their elements into a new set, without duplicating any elements.
For instance, if we have the sets \( A = \{1, 3, 5\} \) and \( B = \{2, 3, 4\} \), the union \( A \cup B \) would be \( \{1, 2, 3, 4, 5\} \). Notice how each number appears only once in the union set, despite \( 3 \) being present in both sets A and B.
For instance, if we have the sets \( A = \{1, 3, 5\} \) and \( B = \{2, 3, 4\} \), the union \( A \cup B \) would be \( \{1, 2, 3, 4, 5\} \). Notice how each number appears only once in the union set, despite \( 3 \) being present in both sets A and B.
- In combining the elements of \( A \) and \( B \), one must ensure no element repeats in \( A \cup B \).
- The concept of union is widely used in various fields: computer science, database management, and of course, probability theory.
- Visualizing sets as overlapping circles in diagrams, often called Venn diagrams, can help grasp the idea of union.
Probability Calculation
Probability calculation involves assigning a numerical value to how likely an event is to occur. When dealing with events expressed as sets, understanding their union - like \( A \cup B \) - helps in determining the probability of any of the events occurring.
To calculate the probability of a union of sets, you would add together the probabilities of all distinct elements within the union. Let's break it down with our example:
To calculate the probability of a union of sets, you would add together the probabilities of all distinct elements within the union. Let's break it down with our example:
- The probability of each element reflects how likely that particular outcome is, with all probabilities in the universal set \( \Omega \) summing to 1.
- The given probabilities were \( P(1)=0.1 \), \( P(2)=0.2 \), \( P(3)=P(4)=0.05 \). The missing probability \( P(5) \) was calculated as \( 1 - (0.1 + 0.2 + 0.05 + 0.05) = 0.6 \).
- Therefore, the probability of the union \( A \cup B \) was \( 0.1 + 0.2 + 0.05 + 0.05 + 0.6 = 1.0 \).