Mathematics | Problems On Permutations | Set 1
Last Updated :
30 Jul, 2024
Permutations are a fundamental concept in combinatorics, dealing with the arrangement of objects in a specific order. In mathematical terms, a permutation is an arrangement of a set of elements in a particular sequence or order. Understanding permutations is crucial not only in mathematics but also in various fields of engineering where precise arrangement and ordering are essential.
What is a Permutation?
Permutation of a set is a specific arrangement of its elements. For a set with n distinct elements, the number of permutations of these elements ( the number of ways in which we can select these n elements ) is given by n! (n factorial). This factorial notation denotes the product of all positive integers up to n.
Types of Permutations
- Simple Permutations: In simple permutations, all elements are unique, and each arrangement is distinct.
- Permutations with Repetition: When elements can repeat, the number of permutations changes based on the repetition of elements.
Permutations formula:
1. P(n, r) = n! / (n-r)! ( Selecting r item form a collection of n items)
2. P(n, n) = n! ( Selecting n item form a collection of n items)
Formula Problems on Permutation
Example 1:
How many 4-letter words, with or without meaning, can be formed out of the letters of the word, 'GEEKSFORGEEKS', if repetition of letters is not allowed ?
Explanation :
Total number of letters in the word 'GEEKSFORGEEKS' = 13 Therefore, the number of 4-letter words
= Number of arrangements of 13 letters, taken 4 at a time.
= 13P4
Example 2:
How many 4-digit numbers are there with distinct digits ?
Explanation :
Total number of arrangements of ten digits ( 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ) taking 4 at a time
= 10P4
These arrangements also have those numbers which have 0 at thousand's place. (For eg- 0789 which is not a 4-digit number.). If we fix 0 at the thousand's place, we need to arrange the remaining 9 digits by taking 3 at a time. Total number of such arrangements
= 9P3
Thus, the total number of 4-digit numbers
= 10P4 - 9P3
Example 3:
How many different words can be formed with the letters of the word "COMPUTER" so that the word begins with "C" ?
Explanation :
Since all the words must begin with C. So, we need to fix the C at the first place. The remaining 7 letters can be arranged in
= 7P7
= 7! ways.
Example 4:
In how many ways can 8 C++ developers and 6 Python Developers be arranged for a group photograph if the Python Developers are to sit on chairs in a row and the C++ developers are to stand in a row behind them ?
Explanation:
6 Python Developers can sit on chairs in a row in
= 6P6
= 6! ways 8 C++ Developers can stand behind in a row in
= 8P8
= 8! ways Thus, the total number of ways
= 6! x 8! ways
Example 5:
Prove that 0! = 1.
Explanation :
Using the formula of Permutation-
P(n, r) = n! / (n-r)!
P(n, n) = n! / 0! (Let r = n )
n! = n! / 0! (Since, P(n, n) = n!)
0! = n! / n!
0! = 1
Thus, Proved
Practice Problems on Permutations
1).How many 4-digit numbers can be formed using the digits 1, 2, 3, 4, 5 without repetition?
2).In how many ways can 7 people be seated in a row if 2 specific people must sit together?
3).How many ways are there to arrange the letters of the word "MATHEMATICS"?
4).In a class of 30 students, in how many ways can a president, secretary, and treasurer be chosen?
5).How many 5-letter words can be formed from the letters of "EQUATION" if each letter can be used only once?
6).In how many ways can 8 different books be arranged on a shelf if 3 specific books must always be next to each other?
7).How many different 6-digit numbers can be formed using the digits 0, 1, 2, 3, 4, 5 if the number must be even?
8).In how many ways can 5 men and 4 women be seated in a row if no two women sit together?
9).How many ways are there to distribute 5 distinct prizes among 10 people?
10).In how many ways can the letters of the word "MISSISSIPPI" be arranged?
Read More: Permutations and Combinations
Applications in Engineering
Permutations find applications in various engineering disciplines:
- Computer Science: In algorithms and data structures, permutations are used for generating all possible orders of elements.
- Telecommunications: Permutations are applied in coding theory and signal processing for efficient data transmission.
- Manufacturing: Permutations help in scheduling and optimizing production sequences on assembly lines.
Conclusion
Permutations are a powerful mathematical tool with wide-ranging applications in engineering it also enables engineers to solve complex problems involving arrangement and optimization. From optimizing manufacturing processes to enhancing data transmission efficiency, understanding permutations enhances problem-solving skills but also facilitates innovation and efficiency across various engineering disciplines. By mastering the principles of permutations, engineers can innovate solutions that drive technological advancements across various industries.
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