About how many people would need to be gathered together to be at least 50% sure that two of them will share the same birthday (the same day of the year, not necessarily the same year)?
A)4
B)23
C)183
D)2,300 or more

Question

Quizplus · Accepted Answer

This is known as the birthday problem or birthday paradox. With 23 people, there are 253 possible pairs of people (23 choose 2). The probability that two people do not share the same birthday is (364/365)^253, which is approximately 0.49 or 49%. Therefore, the probability that at least two people share the same birthday is 1 - 0.49 = 0.51 or 51%, which is just over 50%.

About How Many People Would Need to Be Gathered Together