How many non-negative integer solutions are there to the equation rị + *2 + x3 = 21

A First Course in Probability (10th Edition)
10th Edition
ISBN:9780134753119
Author:Sheldon Ross
Publisher:Sheldon Ross
Chapter1: Combinatorial Analysis
Section: Chapter Questions
Problem 1.1P: a. How many different 7-place license plates are possible if the first 2 places are for letters and...
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**Problem Statement: Finding Non-Negative Integer Solutions**

**Question:**

How many non-negative integer solutions are there to the equation

\[ x_1 + x_2 + x_3 = 21 \]

**Detailed Explanation:**

This problem asks us to find the number of non-negative integer solutions for the given linear Diophantine equation. In other words, we need to determine the number of ways we can assign values to \( x_1 \), \( x_2 \), and \( x_3 \) such that their sum equals 21.

This type of problem is a classic combinatorial problem that can be solved using the "stars and bars" theorem. The stars and bars theorem is used to determine the number of ways to distribute \( n \) identical items into \( k \) distinct groups.

In this context:

- The "stars" represent the total number of items to be divided, which is 21.
- The "bars" will be used to divide these items into 3 distinct groups (representing \( x_1 \), \( x_2 \), and \( x_3 \)).

The formula to determine the number of ways to place \( n \) items into \( k \) groups is given by the combination:

\[ \binom{n + k - 1}{k - 1} \]

In our case:

- \( n = 21 \) (the total sum we want to achieve)
- \( k = 3 \) (the number of variables or groups)

Thus, the number of solutions is:

\[ \binom{21 + 3 - 1}{3 - 1} = \binom{23}{2} \]

Calculating this combination, we get:

\[ \binom{23}{2} = \frac{23!}{2!(23 - 2)!} = \frac{23 \times 22}{2 \times 1} = 253 \]

Therefore, there are 253 non-negative integer solutions to the equation \( x_1 + x_2 + x_3 = 21 \).
Transcribed Image Text:**Problem Statement: Finding Non-Negative Integer Solutions** **Question:** How many non-negative integer solutions are there to the equation \[ x_1 + x_2 + x_3 = 21 \] **Detailed Explanation:** This problem asks us to find the number of non-negative integer solutions for the given linear Diophantine equation. In other words, we need to determine the number of ways we can assign values to \( x_1 \), \( x_2 \), and \( x_3 \) such that their sum equals 21. This type of problem is a classic combinatorial problem that can be solved using the "stars and bars" theorem. The stars and bars theorem is used to determine the number of ways to distribute \( n \) identical items into \( k \) distinct groups. In this context: - The "stars" represent the total number of items to be divided, which is 21. - The "bars" will be used to divide these items into 3 distinct groups (representing \( x_1 \), \( x_2 \), and \( x_3 \)). The formula to determine the number of ways to place \( n \) items into \( k \) groups is given by the combination: \[ \binom{n + k - 1}{k - 1} \] In our case: - \( n = 21 \) (the total sum we want to achieve) - \( k = 3 \) (the number of variables or groups) Thus, the number of solutions is: \[ \binom{21 + 3 - 1}{3 - 1} = \binom{23}{2} \] Calculating this combination, we get: \[ \binom{23}{2} = \frac{23!}{2!(23 - 2)!} = \frac{23 \times 22}{2 \times 1} = 253 \] Therefore, there are 253 non-negative integer solutions to the equation \( x_1 + x_2 + x_3 = 21 \).
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