which works well for probabilities less than or equal to . In these equations, is the number of days in a year.

For instance, to estimate the number of people required for a chance of a shared birthday, we get

Which is not too far from the correct answer of 23.

Approximation of number of people

This can also be approximated using the following formula for the number of people necessary to have at least a chance of matching:
:This is a result of the good approximation that an event with probability

1.Previous
3.Next