<Dd> n ≈ 2 m × p (n) (\ displaystyle n \ approx (\ sqrt (2m \ times p (n)))) </Dd> <P> which works well for probabilities less than or equal to 1 / 2 . In these equations, m is the number of days in a year . </P> <P> For instance, to estimate the number of people required for a 1 / 2 chance of a shared birthday, we get </P> <Dl> <Dd> n ≈ 2 × 365 × 1 2 = 365 ≈ 19 (\ displaystyle n \ approx (\ sqrt (2 \ times 365 \ times (\ tfrac (1) (2)))) = (\ sqrt (365)) \ approx 19) </Dd> </Dl>

Chances of having the same birthday as someone else