christoph wrote:

How many randomly assembled ppl do u need to have a better than 50% prob. that at least 1 of them was born in a leap year ?

prob of being born in a leap year is 1/4 and not being born in a leap year is 3/4

(note: if considering days of birth, than probabilities will be slightly different because leap year has 366 days, so prob of being born on a leap year is 366/(3*365+366) = approx 1/4 )

prob(none out of n people is born in a leap year) is (3/4)^n

so

prob(at least one of them is born in a leap year) = 1-(3/4)^n >1/2 => (3/4)^n < 1/2

minimum number of people is 3 (n=3).