Selection with Repetition

Selection with Repetition

## Definition / Concept

When $$r$$ objects are selected from $$n$$ types and repetition is allowed, the number of selections is:

$$^{n+r-1}C_r$$

Equivalently:

$$^{n+r-1}C_{n-1}$$

## Usage

- Used when identical objects of each type can be selected repeatedly and order does not matter.