1 class has at least?? peoples for probability has at least 2 people with the same birthday?

Question

a.>=21 b.>22 c.>=23 d.>24 (1 year has 365 days)

Answer 1

http://mathforum.org/dr.math/faq/faq.birthdayprob.html

Answer 2

I'm not totally sure what you are asking but if a class has k people, then the probability that at least two people share the same birthday is

P(At least two have same birthday) = 1 - P(None have the same birthday)
= 1 - (365/365)(364/365)(363/365)...
*(365-k+1)/365

If I remember correctly, this probability becomes larger than 0.5 when k = 23.

Answer 3

I think you are asking what is the smallest size class where the probability will favor at least two people having the same birthday

if you were trying to find the probability that 2 people had the same birthday and you named the day, say september 5, that probability would be quite low

however, this problem allows the day to be any day

so, the question is way more complicated

this website gives a very detailed explanation of the calculation

http://mathforum.org/dr.math/faq/faq.birthdayprob.html

the answer is 23

Answer 4

I assume you mean the probability is 50% or more that 2 people share the same birthday.
If so, the answer is c.
with 23 people the probability is 50.729723432 %
or 1 - (365/365)(364/365)(363/365) ... (343/365) > .5
(with 22 people its only 47.5695307..%