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Let \(E\) and \(F\) be mutually exclusive events and suppose \(P(F) \neq 0\). Find \(P(E \mid F)\) and interpret your result.

Short Answer

Expert verified
The conditional probability of event E happening, given that event F has already happened, is 0, \(P(E \mid F) = 0\). This means that if event F occurs, there is no chance of event E happening since they are mutually exclusive events, and their occurrence is completely independent of each other.

Step by step solution

01

Understand mutually exclusive events

Two events E and F are called mutually exclusive events if and only if they cannot both occur at the same time. In other words, if event E occurs, event F cannot occur, and vice versa. Mathematically, for mutually exclusive events, their intersection (E ∩ F) is an empty set, which means the probability of their intersection is zero: \(P(E \cap F) = 0\).
02

Understand conditional probability

Conditional probability is the probability of an event occurring, given that another event (by assumption, presumption, assertion or evidence) has already occurred. In this case, we want to find the probability of event E happening, given that event F has already happened. The formula for conditional probability is: \(P(E \mid F) = \frac{P(E \cap F)} {P(F)}\)
03

Apply the concepts to find the solution

Now we'll use the concepts of mutually exclusive events and conditional probability to find the solution. Since events E and F are mutually exclusive, their intersection has a probability of 0: \(P(E \cap F) = 0\) We already know that the probability of event F is non-zero, so we can use the conditional probability formula: \(P(E \mid F) = \frac{P(E \cap F)} {P(F)} = \frac{0}{P(F)} = 0\) So, the conditional probability of event E happening, given that event F has already happened, is 0.
04

Interpret the result

This result implies that if event F occurs, there is no chance of event E happening since they are mutually exclusive events. In other words, the occurrence of mutually exclusive events is completely independent of each other, and knowing that one of the events has occurred does not provide any information about the other event's occurrence.

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Key Concepts

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

Conditional Probability
Conditional probability is the measure of the likelihood of one event occurring with some relationship to one or more other events. When you're told that one event, say Event F, has occurred, this information can affect the probability of another event, say Event E, happening. The formula for conditional probability is given by:
\( P(E | F) = \frac{P(E \cap F)}{P(F)} \)
This formula states that the probability of E occurring given F has occurred is the ratio of the probability of both E and F occurring to the probability of F occurring. However, in our exercise, since E and F are mutually exclusive, they can't happen together.

Understanding the Implications

Knowing that Events E and F cannot occur at the same time is crucial. Hence, the conditional probability of E given F is simply 0 because the occurrence of F entirely rules out the occurrence of E. This is a key concept for tackling problems involving mutually exclusive events; by knowing the nature of the relationship between events, their probabilities can be effectively calculated.
Probability of an Intersection
The probability of an intersection refers to the likelihood of two events both taking place at the same time. For independent events, calculating this probability involves multiplying the probability of each event occurring separately. The general formula for the probability of the intersection of two events E and F is:
\( P(E \cap F) = P(E) \times P(F) \)
But what about when events are mutually exclusive, like in our textbook example? For mutually exclusive events, the intersection is empty because the events cannot occur together—hence, \(P(E \cap F)=0\).

Real-World Application

Understanding the concept of intersection is practical while dealing with real-life scenarios where events can or cannot happen simultaneously. For instance, drawing a heart and a club from a deck of cards in one pick is impossible—these are mutually exclusive events, just like E and F in our exercise.
Independent Events
Independent events are fundamentally different from mutually exclusive events. Two events are considered independent if the occurrence of one does not affect the probability of the occurrence of the other. One classic example is flipping a coin: whether it lands heads or tails on one flip has no bearing on the results of the next flip.
For independent events, the probability of E given F is simply the probability of E itself since F's occurrence does not influence E. This can be expressed as:
\( P(E | F) = P(E) \)
In the context of our original exercise, although it was mentioned that the occurrence of mutually exclusive events E and F is independent of each other, this isn't a reference to 'independent events' in the typical probabilistic sense. Instead, it means that knowing F occurred gives us no hope of E occurring; they don't influence one another because they simply cannot co-occur.

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Most popular questions from this chapter

At a certain medical school, \(\frac{1}{7}\) of the students are from a minority group. Of those students who belong to a minority group, \(\frac{1}{3}\) are black. a. What is the probability that a student selected at random from this medical school is black? b. What is the probability that a student selected at random from this medical school is black if it is known that the student is a member of a minority group?

Determine whether the statement is true or false. If it is true, explain why it is true. If it is false, give an example to show why it is false. If \(A\) is a subset of \(B\) and \(P(B)=0\), then \(P(A)=0\).

If a certain disease is present, then a blood test will reveal it \(95 \%\) of the time. But the test will also indicate the presence of the disease \(2 \%\) of the time when in fact the person tested is free of that disease; that is, the test gives a false positive \(2 \%\) of the time. If \(0.3 \%\) of the general population actually has the disease, what is the probability that a person chosen at random from the population has the disease given that he or she tested positive?

In a survey on consumer-spending methods conducted in 2006, the following results were obtained: $$\begin{array}{lccccc} \hline & & & & {\text { Debit/ATM }} & \\ \text { Payment Method } & \text { Checks } & \text { Cash } & \text { Credit cards } & \text { cards } & \text { Other } \\ \hline \text { Transactions, \% } & 37 & 14 & 25 & 15 & 9 \\ \hline \end{array}$$ If a transaction tracked in this survey is selected at random, what is the probability that the transaction was paid for a. With a credit card or with a debit/ATM card? b. With cash or some method other than with a check, a credit card, or a debit/ATM card?

The Office of Admissions and Records of a large western university released the accompanying information concerning the contemplated majors of its freshman class:3 $$\begin{array}{lccc} \text { Major } & \text {This Major, \% } & \text { Females, \% } & \text { Males, \% } \\ \hline \text { Business } & 24 & 38 & 62 \\ \hline \text { Humanities } & 8 & 60 & 40 \\ \hline \text { Education } & 8 & 66 & 34 \\ \hline \text { Social science } & 7 & 58 & 42 \\ \hline \text { Natural sciences } & 9 & 52 & 48 \\ \hline \text { Other } & 44 & 48 & 52 \\ \hline \end{array}$$ What is the probability that a. A student selected at random from the freshman class is a female? b. A business student selected at random from the fresh- man class is a male? c. A female student selected at random from the freshman class is majoring in business?

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