Combination with Replacement Calculator

  • Enter 'n' (total items) and 'r' (selection count).
  • Check "Allow Zero Selection" if needed.
  • Click "Calculate" to compute the result.
  • View the result and calculation details below.
  • Use "Calculation History" to track previous calculations.
  • Click "Clear" to reset the inputs and results.
  • Click "Copy Result" to copy the result to the clipboard.
Advanced Features

Calculation Details

Calculation History

What is Combination with Replacement?

Combination with replacement is a concept in combinatorics that refers to the number of ways to select a certain number of items from a set, allowing for the possibility of selecting the same item more than once (with replacement).

All Formulae Related to Combination with Replacement

  1. Number of Combinations with Replacement: The number of ways to choose ‘r’ items from a set of ‘n’ distinct items with replacement is given by the formula:scssCopy codeC(n + r - 1, r) Where:
    • C(n, k) represents the binomial coefficient, calculated as C(n, k) = n! / (k! * (n – k)!).
    • ‘n’ is the total number of distinct items in the set.
    • ‘r’ is the number of items to be selected from the set.
  2. Number of Combinations with Replacement (Repetition Allowed): If you have ‘n’ types of objects, and you want to choose ‘r’ objects from them with replacement, the formula for the number of combinations is:Copy coden^r Where ‘n’ is the number of distinct types of objects, and ‘r’ is the number of objects to be chosen.
  3. Total Combinations with Limited Choices: If you have ‘n’ types of objects, and you want to choose ‘r’ objects from them with replacement, but you can choose from only ‘k’ distinct types of objects (k ≤ n), then the formula is:Copy codek^r Where ‘k’ is the number of distinct types of objects you can choose from, and ‘r’ is the number of objects to be chosen.
  4. Total Combinations of N Objects with R Repeated: If you have ‘n’ objects in total, and you want to choose ‘r’ of them with replacement, and each object can be repeated a maximum of ‘m’ times (0 ≤ m ≤ r), then the formula is:scssCopy codeC(r + n - 1, r - m) Where:
    • ‘n’ is the number of distinct objects.
    • ‘r’ is the total number of objects to be chosen.
    • ‘m’ is the maximum number of times an object can be repeated in the selection.


A Combination with Replacement calculator or the concept itself can be applied in various fields and situations where you need to count or calculate the number of possible outcomes or combinations when selecting items with replacement. Here are some applications across different domains:

  1. Probability and Statistics:
    • In probability theory, combination with replacement is used to calculate the probability of certain outcomes in experiments with replacement, such as drawing cards or selecting items from a population.
  2. Sampling and Surveys:
    • When conducting surveys or sampling from a population, combination with replacement helps in determining the number of different samples that can be obtained, considering that each item can be selected more than once.
  3. Inventory Management:
    • In inventory management, it is essential to calculate the number of ways to select items from a stock with replacement. This is useful for optimizing stock levels and predicting future demand.
  4. Genetics and Biology:
    • In genetics, combination with replacement is used in modeling genetic inheritance and population genetics. It helps in understanding how alleles are passed from one generation to the next, considering the possibility of multiple offspring inheriting the same allele from a parent.
  5. Chemistry and Chemical Engineering:
    • In chemistry, combination with replacement can be applied to chemical reactions and mixing solutions, where multiple reactions or combinations are possible with the same reactants.
  6. Data Science and Machine Learning:
    • In machine learning, especially when working with bootstrapping techniques, combination with replacement is used to generate multiple resamples of a dataset with replacement. This is crucial for building robust models and estimating uncertainties.


Using a Combination with Replacement Calculator offers several benefits across different fields and applications. Here are some of the key advantages:

  1. Accuracy: Calculating combinations with replacement manually can be prone to errors, especially for large values of ‘n’ and ‘r.’ A calculator ensures accurate results every time, reducing the risk of mistakes.
  2. Efficiency: Computationally intensive tasks involving large datasets or numerous combinations can be time-consuming when done by hand. A calculator performs calculations quickly, saving time and effort.
  3. Complex Scenarios: Combination with replacement calculators can handle complex scenarios with ease, including situations where there are multiple distinct types of items or where items have varying maximum repetition limits.
  4. Versatility: These calculators can be used in various fields, from probability and statistics to genetics and finance, making them versatile tools for solving a wide range of problems.
  5. Exploration: Calculators allow you to explore different scenarios by quickly adjusting the input values, making it easier to analyze how changing parameters affect outcomes.
  6. Educational Tool: Combination with replacement calculators are valuable tools for teaching and learning combinatorics and probability theory. They provide students with a practical way to understand and apply mathematical concepts.

Last Updated : 27 February, 2024

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21 thoughts on “Combination with Replacement Calculator”

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