How many derangements are possible of the set {1,2,3,4} O 6 O 7 O 8
Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
Problem 1PE
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![**Question:**
How many derangements are possible for the set {1, 2, 3, 4}?
**Options:**
- ○ 6
- ○ 7
- ○ 8
- ● 9
**Explanation:**
In combinatorics, a derangement is a permutation of the elements of a set, such that no element appears in its original position. For the given set {1, 2, 3, 4}, the number of derangements can be calculated using the formula for derangements:
\[ !n = n! \sum_{i=0}^{n} \frac{(-1)^i}{i!} \]
Applying this formula for \( n = 4 \):
\[ !4 = 4! \left(\frac{1}{0!} - \frac{1}{1!} + \frac{1}{2!} - \frac{1}{3!} + \frac{1}{4!}\right) \]
\[ = 24 \left( 1 - 1 + 0.5 - \frac{1}{6} + \frac{1}{24} \right) \]
\[ = 24 \left( 0.5 - 0.1667 + 0.0417 \right) \]
\[ = 24 \left( 0.375 \right) \]
\[ = 9 \]
Thus, the correct answer is 9 derangements.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fb89e603e-61c2-4a4b-a30b-7e019f65a9c9%2F859649f7-5a90-4f1c-b8e9-875fec02f6f5%2Feppc6q_processed.png&w=3840&q=75)
Transcribed Image Text:**Question:**
How many derangements are possible for the set {1, 2, 3, 4}?
**Options:**
- ○ 6
- ○ 7
- ○ 8
- ● 9
**Explanation:**
In combinatorics, a derangement is a permutation of the elements of a set, such that no element appears in its original position. For the given set {1, 2, 3, 4}, the number of derangements can be calculated using the formula for derangements:
\[ !n = n! \sum_{i=0}^{n} \frac{(-1)^i}{i!} \]
Applying this formula for \( n = 4 \):
\[ !4 = 4! \left(\frac{1}{0!} - \frac{1}{1!} + \frac{1}{2!} - \frac{1}{3!} + \frac{1}{4!}\right) \]
\[ = 24 \left( 1 - 1 + 0.5 - \frac{1}{6} + \frac{1}{24} \right) \]
\[ = 24 \left( 0.5 - 0.1667 + 0.0417 \right) \]
\[ = 24 \left( 0.375 \right) \]
\[ = 9 \]
Thus, the correct answer is 9 derangements.
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