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Combina

COMBINA Function

The COMBINA function in Excel is used to calculate the number of combinations (or subsets) that can be created by selecting a specific number of items from a larger set, with repetitions allowed. This function is useful in probability, statistics, or combinatorial analysis when repetition is considered.

Syntax:

COMBINA(number, number_chosen)
  • number: This is a required argument. It specifies the total number of items in the set.
  • number_chosen: This is a required argument. It specifies the number of items to choose from the set (with repetition allowed).

The function calculates combinations with repetition using the formula:

COMBINA(number, number_chosen) = (number + number_chosen - 1)! / 
                                  (number_chosen! * (number - 1)!)

Examples:

  1. =COMBINA(5, 2)
    Calculates the number of ways to choose 2 items from a set of 5 items, allowing repetition.
    Result: 15

  2. =COMBINA(4, 3)
    Calculates the number of ways to choose 3 items from a set of 4 items, allowing repetition.
    Result: 20

  3. =COMBINA(3, 1)
    Calculates the number of ways to choose 1 item from a set of 3 items, allowing repetition.
    Result: 3

Notes:

  • The COMBINA function works only with non-negative integers. If either argument is non-integer or negative, Excel will return a #NUM! error.
  • The number_chosen argument must be greater than or equal to 0, or the function will return a #NUM! error.
  • Unlike COMBIN, the COMBINA function accounts for repetitions, making it suitable for scenarios where items can be selected multiple times.

Tip: Use the COMBINA function to calculate scenarios involving repeated selections, such as arrangements of colored balls where each color can be chosen multiple times.