**139 birthday questions.**

there are 12 signs of zodiac. how many people must be present for there to be at least a 50% chance that two or more of them were born under the same sign.
im not sure what formula i should be using ...

Say you have n randomly selected students from another planet whose birthdays are known. x of them have birthdays that collide with at least one other student. How do you estimate the number of days ...

I have a question concerning the birthday problem in conditional problem. Say there's a given group of $12$ people and a regular year with only $365$ days. Then the probability of no duplicate will be ...

If there are 100 people in a room then what is the probability that at least 2 of them share birthdays? I read that answer should be $1-\left(\frac{365!}{265!\times365^{100}} \right)$, and I ...

In birthday problem say total number of people n < 365, then probability of all person having distinct birthday is given by,
$$\frac{\text{total no. of ways of selecting $n$ numbers from $365$ ...

I learned about the birthday paradox or birthday problem in school, and it was pretty intriguing. I finished all my homework for said class but I am stuck one specific question, which is supposed to ...

Sorry I am new here and learning mathematics and cryptographic problems.
Assume an hash algorithm is collision resistant like SHA256, and the hash value is 64bit in length, (2^{64} possibilities)
...

Suppose that a child desires $10$ different toys for her birthday.
Twenty people will come to her birthday party, each of them equally likely to bring any one of the $10$ toys.
Let $X$ be the ...

Four people around a room. What is the probability that two (or more) of them have the same birthday?
However, I am not sure if my working out assume finds out about the 2 or more part. I am using ...

The Birthday Problem: given $n$ people (typically $n<365$), what is the probability that some pair of them share a birthday (omitting Feb 29th, for simplicity)?
The solution: First, find the ...

$11$ numbers between $1$ and $40$ are select. What is the probability there are some duplicated integers in those $11$?
I think the answer to this question is very straightforward: $1-P(\text{they ...

Question
People are arriving at a party one at a time. While waiting for more people to arrive
they entertain themselves by comparing their birthdays. Let X be the number of people
needed to obtain a ...

How would I calculate the probability of atleast 2 people having the same birthday given a group of 3 using counting principles. I know that using P(same bday) = 1 - P(not same bday). I calculated ...

In repeated uniform sampling from $\{1,\dots,n\}$ the mean time $E(X)$ to find the first duplicate is asymptotically $\sqrt{n\pi/2}$. What about the variance?
The variance is $E(X^2) -E(X)^2$.
$...

I asked a somewhat related question recently and then became interested in this one: how many people are required, on average, until 3 share a birthday? More generally, if we have $M$ bins, what is ...

What is the formula for the birthday problem?
I can't seem to find JUST the formula. I don't care how it works at this point, I just want to know what to do. Can someone please just tell me? Most ...

I need help with an approximation concerning the birthday problem. In a recent MAA Monthly (August-September 2013) article "Simple Approximation Formulas for the Birthday Problem" by Matthias Arnold ...

I find out that the problem I'm trying to solve is related to Birthday problem, specifically to collision counting:
$$c = n - d + d(\frac{d-1}{d})^n$$
In my case, I know the desired number of ...

I'm having trouble attempting this question. In a group of $n$ people, what is the probability that at least $3$ have the same birthday?
I started off by saying Pr(At least $3$) $= 1 -$ (Pr(no $3$) +...

Question: whats the probability that at least 3 out of a group of n people have the same birthday.
I am confused as to where to start. I know that it would be complementary probability, but even then ...

This question is about the birthday problem: the probability that in a group of n people, at least two of them have the same birthday (https://en.wikipedia.org/wiki/Birthday_problem).
An easy way to ...

For a group of $100$ random people, find:
The expected number of days that are the birthday of at least 3 people, birthyear not being significant.
The expected number of distinct birthday days.
(...

I was trying to work through the Birthday problem with the assumptions that
($1$) February $29$th is excluded as a possible birthday, and
($2$) All days are equally likely for birthdays to occur,
...

I am trying to figure out that what is the probability that at least 40 people share the same birthday out of 350? Calculator gives an error when I try to calculate $^{365}P_{40}$. Please help!

The other night I was hanging out with some friends and someone put on a playlist on shuffle random, where the songs are drawn uniformly at random from a fixed playlist. The person who put the ...

I want to solve a variation on the Coupon Collector Problem, or (alternately) a slight variant on the standard Birthday Problem.
I have a slight variant on the standard birthday problem.
In the ...

This is for the probability that in a group of n people at least two have the same birthday, n = 3.
Hi, So for those who are familiar with the birthday paradox could you check my work:).
P(E) = [...

What is the probability that from 23 at least people 2 people have their birthday on the same day. Assume that the year has 365 days and that all the birthday combinations have the same probability.
...

How many people must there be before the chances that someone
has the same birthday as you do is at least 0.5? How many people must there be
before the chances that at least two people have a birthday ...

Consider the birthdays of a group of k people, 2<_k<_365. Assume the birthdays are unrelated
and each of the 365 days is equally likely to be the birthday of any person in the group. What is ...

In a party of 5 persons compute the probability that at least 2 have the same birthday(month/day),assume a 365-day year.

My question is: Find the probability that at least 2 people in a room of 30 share the same birthday.
I looked at this problem - Having birthday at the same day after watching the Birthday Probability ...

There are 17 people. We assume that a year has 365 days.
a) What is the probability that at least two of them have birthday at the same day of the year?
b) What is the probability that exactly two ...

Let $X, Y$ be finite sets with $|Y|= n$ and $f: X \to Y$ such that all preimages $f^{-1}(y),\,y\in Y$ have the same cardinality.
A pair $x_1 \neq x_2$ in $X$ such that $f(x_1)=f(x_2)$ is called a ...

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