Applying the Stars and Bars Method to the Problem

Oct 13, 2025 by wbrum.org 94 views

Introduction

Distributing identical gold coins among a group of people is a classic problem in combinatorics. In this article, we will explore the number of ways in which 15 identical gold coins can be distributed among 3 persons such that each one gets at least 3 gold coins. This problem involves the concept of distributing identical objects into distinct groups, which is a fundamental idea in combinatorics.

Background

The problem of distributing identical objects into distinct groups is a well-studied topic in combinatorics. There are several methods to solve this problem, including the use of generating functions, the stars and bars method, and the principle of inclusion-exclusion. In this article, we will use the stars and bars method to solve the problem.

The Stars and Bars Method

The stars and bars method is a combinatorial technique used to count the number of ways to distribute identical objects into distinct groups. The method involves representing the objects as stars and the dividers between the groups as bars. For example, if we have 5 identical objects and 2 groups, we can represent the distribution as follows:

- | *

In this representation, the stars represent the objects and the bars represent the dividers between the groups. The number of ways to distribute the objects is equal to the number of ways to arrange the stars and bars.

Applying the Stars and Bars Method to the Problem

To apply the stars and bars method to the problem of distributing 15 identical gold coins among 3 persons such that each one gets at least 3 gold coins, we need to represent the coins as stars and the dividers between the groups as bars. Since each person must get at least 3 coins, we can represent the distribution as follows:

- - | * * * | * * *

In this representation, the first three stars represent the coins given to the first person, the next three stars represent the coins given to the second person, and the last three stars represent the coins given to the third person. The bars represent the dividers between the groups.

Counting the Number of Ways to Distribute the Coins

To count the number of ways to distribute the coins, we need to count the number of ways to arrange the stars and bars. Since there are 15 stars and 2 bars, we can represent the distribution as a string of 17 characters, consisting of 15 stars and 2 bars. The number of ways to arrange the stars and bars is equal to the number of ways to choose 2 positions out of 17 for the bars.

Calculating the Number of Ways to Choose the Bars

The number of ways to choose 2 positions out of 17 for the bars is given by the binomial coefficient:

C(17, 2) = 17! / (2! * 15!)

where C(n, k) is the binomial coefficient, which represents the number of ways to choose k positions out of n.

Evaluating the Binomial Coefficient

To evaluate the binomial coefficient, we can use the formula:

C(n, k) = n! / (k! * (n-k)!)

where n! is the factorial of n.

Calculating the Factorials

To calculate the factorials, we can use the following formulas:

n! = n * (n-1) * ... * 2 * 1

where n is a positive integer.

Evaluating the Factorials

To evaluate the factorials, we can use the following values:

15! = 15 * 14 * ... * 2 * 1 = 1307674368000 17! = 17 * 16 * ... * 2 * 1 = 355687428096000 2! = 2 * 1 = 2 15! = 15 * 14 * ... * 2 * 1 = 1307674368000

Substituting the Values into the Formula

To substitute the values into the formula, we get:

C(17, 2) = 17! / (2! * 15!) = 355687428096000 / (2 * 1307674368000) = 136

Conclusion

In this article, we have used the stars and bars method to count the number of ways in which 15 identical gold coins can be distributed among 3 persons such that each one gets at least 3 gold coins. We have represented the coins as stars and the dividers between the groups as bars, and counted the number of ways to arrange the stars and bars. We have evaluated the binomial coefficient using the formula, and substituted the values into the formula to get the final answer. The number of ways to distribute the coins is 136.

References

Combinatorics: Topics, Techniques, Algorithms, by Peter J. Cameron
The Art of Combinatorics, by Richard P. Stanley
Combinatorial Mathematics, by Herbert S. Wilf

Introduction

In our previous article, we explored the number of ways in which 15 identical gold coins can be distributed among 3 persons such that each one gets at least 3 gold coins. We used the stars and bars method to count the number of ways to distribute the coins. In this article, we will answer some frequently asked questions related to this problem.

Q: What is the stars and bars method?

A: The stars and bars method is a combinatorial technique used to count the number of ways to distribute identical objects into distinct groups. It involves representing the objects as stars and the dividers between the groups as bars.

Q: How does the stars and bars method work?

A: The stars and bars method works by representing the objects as stars and the dividers between the groups as bars. The number of ways to distribute the objects is equal to the number of ways to arrange the stars and bars.

Q: What is the binomial coefficient?

A: The binomial coefficient is a fundamental concept in combinatorics that represents the number of ways to choose k positions out of n.

Q: How do you calculate the binomial coefficient?

A: The binomial coefficient can be calculated using the formula:

C(n, k) = n! / (k! * (n-k)!)

where n! is the factorial of n.

Q: What is the significance of the binomial coefficient in this problem?

A: The binomial coefficient is used to count the number of ways to choose 2 positions out of 17 for the bars in the stars and bars representation of the problem.

Q: How do you evaluate the factorials in the binomial coefficient formula?

A: The factorials can be evaluated using the following formulas:

n! = n * (n-1) * ... * 2 * 1

where n is a positive integer.

Q: What is the final answer to the problem?

A: The final answer to the problem is 136, which represents the number of ways in which 15 identical gold coins can be distributed among 3 persons such that each one gets at least 3 gold coins.

Q: What are some real-world applications of the stars and bars method?

A: The stars and bars method has many real-world applications, including:

Counting the number of ways to distribute identical objects into distinct groups
Counting the number of ways to choose k positions out of n
Counting the number of ways to arrange objects in a specific order
Counting the number of ways to distribute objects into distinct groups with certain constraints

Q: What are some common mistakes to avoid when using the stars and bars method?

A: Some common mistakes to avoid when using the stars and bars method include:

Not representing the objects as stars and the dividers between the groups as bars
Not counting the number of ways to arrange the stars and bars
Not using the correct formula for the binomial coefficient
Not evaluating the factorials correctly

Q: What are some tips for using the stars and bars method effectively?

A: Some tips for using the stars and bars method effectively include:

Representing the objects as stars and the dividers between the groups as bars
Counting the number of ways to arrange the stars and bars
Using the correct formula for the binomial coefficient
Evaluating the factorials correctly
Checking the final answer for accuracy

Conclusion

In this article, we have answered some frequently asked questions related to the problem of distributing 15 identical gold coins among 3 persons such that each one gets at least 3 gold coins. We have used the stars and bars method to count the number of ways to distribute the coins and have provided some tips and common mistakes to avoid when using this method.