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Ch. 3 - Probability
Larson - Elementary Statistics: Picturing the World 8th Edition
Larson8th EditionElementary Statistics: Picturing the WorldISBN: 9780137493470Not the one you use?Change textbook
Chapter 3, Problem 3.1.23

Finding the Probability of an Event In Exercises 21-24, the probability that an event will not happen is given. Find the probability that the event will happen. 
23. P(E')=3/4

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Step 1: Understand the problem. The probability of the complement of an event, denoted as P(E'), is given as 3/4. You are tasked with finding the probability of the event itself, denoted as P(E).
Step 2: Recall the relationship between the probability of an event and its complement. The sum of the probabilities of an event and its complement is always equal to 1. Mathematically, this is expressed as: P(E) + P(E') = 1.
Step 3: Substitute the given value of P(E') into the equation. Replace P(E') with 3/4 in the formula: P(E) + 3/4 = 1.
Step 4: Solve for P(E). Rearrange the equation to isolate P(E) on one side: P(E) = 1 - 3/4.
Step 5: Simplify the expression to find the probability of the event happening. Perform the subtraction: P(E) = 1 - 3/4. This will give you the final probability value.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Probability of an Event

Probability is a measure of the likelihood that a specific event will occur, expressed as a number between 0 and 1. An event with a probability of 0 means it will not happen, while a probability of 1 indicates certainty. Understanding how to calculate the probability of an event is fundamental in statistics, as it allows for predictions and informed decision-making.
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Probability of Multiple Independent Events

Complementary Events

Complementary events are two outcomes of a single event where one event occurs if and only if the other does not. For any event E, the probability of its complement E' (the event not happening) plus the probability of E must equal 1. This relationship is crucial for calculating probabilities, as it allows us to find the probability of an event by subtracting the probability of its complement from 1.
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Complementary Events

Calculating Probability from Complements

To find the probability of an event occurring when given the probability of it not occurring, you can use the formula P(E) = 1 - P(E'). In the context of the question, if P(E') = 3/4, then P(E) can be calculated as 1 - 3/4, which equals 1/4. This method is a straightforward approach to solving probability problems involving complementary events.
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Related Practice
Textbook Question

According to Bayes’ Theorem, the probability of event A , given that event B has occurred, is

P(A|B) = P(A) * P(B|A)P(A) * P(B|A) + P(A') * P(B|A').

In Exercises 33–38, use Bayes’ Theorem to find P(A|B).

33. P(A) = 2/3, P(A') = 1/3, P(B|A) = 1/5 , and P(B|A') = 1/2

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Textbook Question

Using a Tree Diagram In Exercises 67-70, a probability experiment consists of rolling a six-sided die and spinning the spinner shown at the left. The spinner is equally likely to land on each color. Use a tree diagram to find the probability of the event. Then explain whether the event can be considered unusual.

68. Event B: rolling an odd number and the spinner landing on green

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Textbook Question

"True or False? In Exercises 5 and 6, determine whether the statement is true or false. If it is false, rewrite it as a true statement.

5. If two events are independent, then P(A|B) = P(B)."

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Textbook Question

Finding Classical Probabilities In Exercises 41-46, a probability experiment consists of rolling a 12-sided die numbered 1 to 12. Find the probability of the event.

43. Event C: rolling a number greater than 4

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Textbook Question

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Textbook Question

"According to Bayes’ Theorem, the probability of event A , given that event B has occurred, is

P(A|B) = P(A) * P(B|A)P(A) * P(B|A) + P(A') * P(B|A').

In Exercises 33–38, use Bayes’ Theorem to find P(A|B).

36. P(A) = 0.62, P(A') = 0.38, P(B|A) = 0.41 , and P(B|A') = 0.17 "

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