The birthday experiment is to draw a random sample of size n with replacement from a population of size N. In the applet, the population consists of N balls numbered from 1 to N. We are interested in the event that there is at least one duplication in the sample; the indicator variable of this event is denoted I. On each update, the sample of balls is shown in the first graph; a ball that duplicates a previously chosen ball is shown in red, and otherwise is shown in green. The value of I is recorded on each update in the first table. The discrete probability density function of I is shown in blue in the second graph and is recorded in the second table. On each update, the empirical probability density function of I is shown in red in the second graph and is recorded in the second table. The parameters N and n can be varied with scroll bars.

## Software/Applets used on this page

## Glossary

### density

the ratio of the mass of an object to its volume

### event

any set of possible outcomes of a statistical experiment

### function

A rule that connects one value in one set with one and only one value in another set.

### graph

A diagram showing a relationship between two variables.

The diagram shows a vertical y axis and a horizontal x axis.

The diagram shows a vertical y axis and a horizontal x axis.

### population

A collection, group or set of individuals or objects.

### sample

A collection of sampling units drawn from a sampling frame.

### variable

A value which is unknown and free to vary, often denoted by x or y.

## This question appears in the following syllabi:

Syllabus | Module | Section | Topic | Exam Year |
---|---|---|---|---|

AQA A-Level (UK - Pre-2017) | S1 | Probability | Experimental | - |

AQA AS Maths 2017 | Statistics | Probability | Experimental Probabilities | - |

AQA AS/A2 Maths 2017 | Statistics | Probability | Experimental Probabilities | - |

CBSE XII (India) | Probability | Probability | Repeated independent (Bernoulli) trials and binomial distribution | - |

CBSE XI (India) | Statistics and Probability | Probability | Random experiments, outcomes, sample spaces (set representation) | - |

CCEA A-Level (NI) | S1 | Probability | Experimental | - |

CIE A-Level (UK) | S1 | Probability | Experimental | - |

Edexcel A-Level (UK - Pre-2017) | S1 | Probability | Experimental | - |

Edexcel AS Maths 2017 | Statistics | Probability | Experimental Probabilities | - |

Edexcel AS/A2 Maths 2017 | Statistics | Probability | Experimental Probabilities | - |

I.B. Higher Level | 5 | Probability | Experimental | - |

I.B. Standard Level | 5 | Probability | Experimental | - |

Methods (UK) | M15 | Probability | Experimental | - |

I.B. (MSSL) | 3 | Probability | Experimental | - |

OCR A-Level (UK - Pre-2017) | S1 | Probability | Experimental | - |

OCR AS Maths 2017 | Statistics | Probability | Experimental Probabilities | - |

OCR MEI AS Maths 2017 | Statistics | Probability | Experimental Probabilities | - |

OCR-MEI A-Level (UK - Pre-2017) | S1 | Probability | Experimental | - |

Pre-Calculus (US) | E4 | Probability | Experimental | - |

Pre-U A-Level (UK) | Prob | Probability | Experimental | - |

Scottish (Highers + Advanced) | HS | Probability | Experimental | - |

Scottish Highers | S | Probability | Experimental | - |

Universal (all site questions) | P | Probability | Experimental | - |

WJEC A-Level (Wales) | S1 | Probability | Experimental | - |