# COMBINA

The `COMBINA` function calculates the number of combinations with repetitions of k items taken from a set of n items. This function is useful when you want to calculate the number of possible combinations that can be formed by selecting k items from a set of n items, where repetition of items is allowed.

## Usage

Use the `COMBINA` formula with the syntax shown below, it has 2 required parameters:

Parameters:
1. n (required):
The total number of items in the set.
2. k (required):
The number of items to be selected from the set.

## Examples

Here are a few example use cases that explain how to use the `COMBINA` formula in Google Sheets.

### Calculating the number of possible outcomes

Suppose you want to calculate the number of possible outcomes of a lottery game where a player selects 5 numbers out of 40. You can use the `COMBINA` function to calculate the total number of possible combinations that can be formed by selecting 5 numbers from a set of 40, where repetition of numbers is allowed.

### Calculating the number of unique combinations

Suppose you want to calculate the number of unique combinations of 3 letters that can be formed from the set {A, B, C, D, E}, where repetition of letters is allowed. You can use the `COMBINA` function to calculate the total number of possible combinations and subtract the number of repeated combinations.

### Calculating the number of possible passwords

Suppose you want to calculate the number of possible 4-digit passwords that can be formed using the digits 0-9, where repetition of digits is allowed. You can use the `COMBINA` function to calculate the total number of possible combinations and subtract the number of repeated combinations.

## Common Mistakes

`COMBINA` not working? Here are some common mistakes people make when using the `COMBINA` Google Sheets Formula:

### Incorrect Syntax

Users often forget to include both arguments in the formula or use incorrect syntax, resulting in an error. Ensure that both n and k are included in the formula and separated by a comma.

### Invalid Arguments

Users sometimes include non-numeric or negative values for n and/or k, which will result in an error. Ensure that both n and k are positive integers.

### Incorrect Result

Users may not realize that COMBINA calculates the number of combinations with repetition, not without repetition. Double-check that the result makes sense for the intended purpose.

The following functions are similar to `COMBINA` or are often used with it in a formula:

• `COMBIN`

The `COMBIN` function calculates the number of combinations for a given number of items. A combination is a way of selecting items from a larger set where order does not matter. This function is commonly used in probability and statistics.

• `PERMUT`

The `PERMUT` function returns the number of permutations of a set of objects. A permutation is a way of arranging objects in a specific order. The function takes two arguments: `n`, the total number of objects, and `k`, the number of objects to arrange. The result is the number of possible permutations. This function is commonly used in combinatorics and probability theory.

• `FACT`

The `FACT` formula calculates the factorial of a given number. The factorial of a number is the product of all positive integers from 1 to the given number. This formula is commonly used in probability and combinatorics.

• `BINOMDIST`

The `BINOMDIST` function calculates the probability of a certain number of successes in a fixed number of trials given a constant probability of success for each trial. This function is commonly used in statistical analysis and hypothesis testing.

You can learn more about the `COMBINA` Google Sheets function on Google Support.