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Compute \(P_{5,2}\)

Short Answer

Expert verified
There are 20 permutations.

Step by step solution

01

Understanding Permutations

The notation \(P_{5,2}\) represents the number of permutations of 5 items taken 2 at a time. It refers to the number of different ways to arrange 2 different items selected from a set of 5 items. The formula to calculate permutations \(P(n, r)\) is given by \(\frac{n!}{(n-r)!}\).
02

Substitute Values into Formula

In this exercise, we substitute the values into the permutation formula where \(n=5\) and \(r=2\). This gives us:\[P_{5,2} = \frac{5!}{(5-2)!} = \frac{5!}{3!}.\]
03

Calculate Factorials

First, calculate \(5!\) and \(3!\):\(5! = 5 \times 4 \times 3 \times 2 \times 1 = 120\).\(3! = 3 \times 2 \times 1 = 6\).
04

Compute the Permutation

Using the factorial values calculated, substitute them back into the formula:\[P_{5,2} = \frac{120}{6} = 20.\]Thus, there are 20 ways to arrange 2 items out of 5.

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Key Concepts

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

Factorials
Factorials are fundamental to understanding permutations and many other areas in mathematics. A factorial, denoted by an exclamation mark (!), is the product of all positive integers up to a specified number. For instance, if you want to calculate the factorial of 5, written as 5!, you multiply all whole numbers from 5 down to 1: 5 x 4 x 3 x 2 x 1. This equals 120.

Factorials are used because they allow mathematicians to account for all possible arrangements of a set of items. The calculation of factorials helps you comprehend how many different ways you can arrange a given number of objects. This is essential in calculations involving permutations and combinations.
Combinatorics
Combinatorics is a branch of mathematics focused on counting, arrangement, and combination of objects. It uses various tools like permutations and combinations to solve complex problems about grouping different items.

Permutations, such as the one in our exercise where we compute \(P_{5,2}\), are a vital part of combinatorics. They count the number of ways to order a subset of items from a larger set, where the order matters.

Combinatorics has many real-world applications. It's used in fields like computer science for designing networks, in biology for analyzing genetic combinations, and in business for planning and logistics.
Problem Solving
Problem solving in mathematics involves approaching any challenge methodically and logically. The goal is to find an efficient path from the problem to the solution.

When dealing with permutations, like in our exercise \(P_{5,2}\), you start by understanding the problem: how many ways can we arrange 2 items out of 5? You then apply the appropriate mathematical formula and break down the steps. This general approach can be used in various problem-solving contexts:
  • Analyze the problem to understand it fully.
  • Identify which tools or formulas apply to the scenario.
  • Carefully execute each step of the solution process.
  • Verify your results to make sure they match the problem's requirements.
Problem-solving enhances your mathematical skills and builds strategies that are useful beyond the math world.
Mathematical Notation
Mathematical notation is a symbolic means of writing mathematical concepts and relationships. It's a universal language that allows mathematicians and scientists to understand each other across different languages.

In our exercise, we used specific notation like \(P_{5,2}\). This notation helps in precisely defining the number of permutations of 2 elements from a set of 5, and it simplifies communication by providing a clear, concise way to represent complex mathematical ideas.

Proper understanding of mathematical notation is crucial for effectively learning math. It can initially seem daunting, but these symbols are shortcuts that make solving and understanding large sets of math problems manageable. Once you're comfortable with the notation, you can easily interpret and solve problems using the concise language of mathematics.

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Most popular questions from this chapter

The Eastmore Program is a special program to help alcoholics. In the Eastmore Program, an alcoholic lives at home but undergoes a two-phase treatment plan. Phase I is an intensive group-therapy program lasting 10 weeks. Phase II is a long-term counseling program lasting 1 year. Eastmore Programs are located in most major cities, and past data gave the following information based on percentages of success and failure collected over a long period of time: The probability that a client will have a relapse in phase I is \(0.27\); the probability that a client will have a relapse in phase II is 0.23. However, if a client did not have a relapse in phase I, then the probability that this client will not have a relapse in phase II is \(0.95 .\) If a client did have a relapse in phase I, then the probability that this client will have a relapse in phase II is \(0.70\). Let \(A\) be the event that a client has a relapse in phase \(\mathrm{I}\) and \(B\) be the event that a client has a relapse in phase II. Let \(C\) be the event that a client has no relapse in phase I and \(D\) be the event that a client has no relapse in phase II. Compute the following: (a) \(P(A), P(B), P(C)\), and \(P(D)\) (b) \(P(B \mid A)\) and \(P(D \mid C)\) (c) \(P(A\) and \(B)\) and \(P(C\) and \(D)\) (d) \(P(A\) or \(B)\) (e) What is the probability that a client will go through both phase I and phase II without a relapse? (f) What is the probability that a client will have a relapse in both phase I and phase II? (g) What is the probability that a client will have a relapse in either phase I or phase II?

USA Today gave the information shown in the table about ages of children receiving toys. The percentages represent all toys sold. What is the probability that a toy is purchased for someone (a) 6 years old or older? (b) 12 years old or younger? (c) between 6 and 12 years old? (d) between 3 and 9 years old? A child between 10 and 12 years old looks at this probability distribution and asks, "Why are people more likely to buy toys for kids older than I am (13 and over) than for kids in my age group (10-12)?" How would you respond? $$\begin{array}{l|c} \hline \text { Age (years) } & \text { Percentage of Toys } \\ \hline 2 \text { and under } & 15 \% \\ 3-5 & 22 \% \\ 6-9 & 270 / 6 \\ 10-12 & 14 \% \\ 13 \text { and over } & 22 \% \end{array}$$

For each of the following situations, explain why the combinations rule or the permutations rule should be used. (a) Determine the number of different groups of 5 items that can be selected from 12 distinct items. (b) Determine the number of different arrangements of 5 items that can be selected from 12 distinct items.

You need to know the number of different arrangements possible for five distinct letters. You decide to use the permutations rule, but your friend tells you to use \(5 !\). Who is correct? Explain.

You roll two fair dice, a green one and a red one. (a) What is the probability of getting a sum of \(7 ?\) (b) What is the probability of getting a sum of \(11 ?\) (c) What is the probability of getting a sum of 7 or 11? Are these outcomes mutually exclusive?

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