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In a certain experiment, whenever the event \(A\) occurs, the event \(B\) also occurs. Which of the following statements is true and why? (a) If we know that \(A\) has not occurred, we can be sure that \(B\) has not occurred as well. (b) If we know that \(B\) has not occurred, we can be sure that \(A\) has not occurred as well.

Short Answer

Expert verified
Statement (b) is true. If we know that event \(B\) has not occurred, we can be sure that event \(A\) has not occurred as well because every occurrence of \(A\) also leads to an occurrence of \(B\).

Step by step solution

01

Statement Analysis

When we know that whenever event \(A\) occurs, event \(B\) also occurs, this can be represented as \(A \rightarrow B\). This means every time \(A\) happens, \(B\) is guaranteed to occur.
02

Inferring from the Given Statements (a)

Statement (a) says that if we know \(A\) has not occurred, we can be sure that \(B\) has not occurred as well. However, from \(A \rightarrow B\) we cannot necessarily infer \(\neg A \rightarrow \neg B\). That's because \(A\) causing \(B\) does not guarantee that \(A\) is the only way \(B\) can occur. Thus, statement (a) is not necessarily true.
03

Inferring from the Given Statements (b)

Statement (b) says that if we know \(B\) has not occurred, we can be sure that \(A\) has not occurred as well. If \(B\) does not happen, it's sure that \(A\) wouldn't have happened because we know that \(A\) always leads to \(B\) (from \(A \rightarrow B\)). Thus, \(\neg B \rightarrow \neg A\) is true which means statement (b) is correct.

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Key Concepts

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

Event Dependency
Understanding how events in probability are connected to one another is a key aspect of forecasting outcomes. Event dependency illustrates this connection, indicating that the occurrence of one event may influence or determine the occurrence of another.
When considering event dependency, information about one event helps us predict another, as is the case with the exercise provided. Since event A occurring means event B will also occur, we can say that A is a sufficient condition for B. In easier terms, think of a key and a lock: if you have the right key (A), the lock will open (B). However, this does not necessarily mean that the lock can't be picked or opened with a different key. So, if the lock didn't open (¬µþ), it's certain that you didn't have the right key (¬´¡).
Visually, this is often represented by a directional arrow in diagrams, where A would point to B, illustrating dependency. Understanding these links is crucial not just in solving probability exercises, but also in real-life scenarios where decision-making relies on the intricate relations between different variables or events.
Logical Inference
Making a logical inference means drawing a conclusion based on premises you know to be true. In the context of our problem, logical inference is applied to deduce relationships between events A and B.
Using logical inference, statement (b) makes sense: if B does not occur, A must not have occurred either, because we established that A leads to B. If B is the effect, then without A, the cause, you cannot have the effect. This relies on what is known as the contrapositive in logic, which in simple terms says that if 'whenever it rains, the ground gets wet', then 'if the ground is not wet, it did not rain'. Logical inference is a powerful tool that helps in deducing these kinds of conclusions and is essential in mathematical reasoning, programming, and even daily decision-making.
Probability Theory
Probability theory is the mathematical framework that enables us to analyze random phenomena and calculate the likelihood of various outcomes. It provides the foundation for determining how variables or events influence each other, much like what you see with events A and B in the original exercise.
In this theory, events can be independent, meaning the occurrence of one does not affect the other, or dependent, like in our example, where event A being true guarantees the occurrence of B. Correct application of probability theory requires not only understanding the numerical chances of an event but also the logical structures underlying these chances. By using probability theory, students learn to quantify uncertainty, make predictions, and develop strategies in fields as various as finance, insurance, science, and even sports.

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