# Manuals/calci/BIRTHDAYPROBABILITY

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**BIRTHDAYPROBABILITY (NumberOfDuplicates,TotalNumberOfDays)**

- is any real number.
- is the number of days.

## Description

- This function shows the value of the Birthday probability.
- In , is the additional number of birthday.
- is the number of days.
- Birthday probability is the sum of the probability that an event will happen and the probability that the event won't happen is always 1.
- In a room of 75 there is a 99.9% chance of two people birthday matching.
- To work out the probability there is no two people will have the same birthday,the following rules to be followed to find the probability that two people will share a birthday:

P(two people share birthday) + P(no two people share birthday) = 1 P(two people share birthday) = 1 - P(no two people share birthday).

## Examples

- BIRTHDAYPROBABILITY(3,30) = 0.1384203445582639
- BIRTHDAYPROBABILITY(20,432) = 0.3686145731391096
- BIRTHDAYPROBABILITY(30.3,765) = 0.44899395029084743

## Related Videos

## See Also

## References