# birthday's questions - Chinese 1answer

139 birthday questions.

### -2 how many people for a 50% of two or more have the same sign? [closed]

2 answers, 37 views probability birthday
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 ...

### 5 “reverse birthday problem” - inferring days in the year from collisions in sample [duplicate]

2 answers, 50 views statistics birthday
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 ...

### Computing Conditional Probability on Birthday Problem

1 answers, 36 views probability birthday
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 ...

1 answers, 53 views probability combinatorics birthday
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 ...

### 2 Birthday problem: using $^nC_r$.

4 answers, 383 views probability combinatorics birthday

### -1 Birthday Problem using Complement Probability [duplicate]

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 $3$) +...

### 2 Birthday problem with at least 3 people

2 answers, 253 views discrete-mathematics birthday
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 ...

### 4 Birthday problem: why is this solution wrong?

1 answers, 194 views combinatorics birthday
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 ...

### 2 Expectation of the sum - birthday anniversary problem.

3 answers, 265 views probability birthday
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. (...

### Question regarding the birthday problem

1 answers, 54 views probability birthday
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, ...

### 3 The Birthday Problem (n>30)

1 answers, 223 views probability statistics birthday
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!

### 34 Guessing the length of a playlist on “shuffle random?”

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 ...

### 4 Coupon Problem generalized, or Birthday problem backward.

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 ...

### 1 Birthday paradox solving for small n values?

2 answers, 76 views discrete-mathematics birthday
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 people 2 people have their birthday on the same day? [duplicate]

0 answers, 161 views probability probability-theory birthday
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. ...

### 1 Same birthday question: 2 different variants have same answer?

1 answers, 39 views probability birthday
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 ...

### Probabilities and Birthdays [duplicate]

0 answers, 23 views statistics 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 ...

### -2 compute the probability that at least 2 have the same birthday? [duplicate]

1 answers, 1.632 views probability birthday
In a party of 5 persons compute the probability that at least 2 have the same birthday(month/day),assume a 365-day year.

### -1 Probability of 2 or more people sharing same birthday given 365 days

2 answers, 837 views probability birthday
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 ...

### 2 Having birthday at the same day

1 answers, 594 views probability combinatorics birthday
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 ...

### Mathematics of the birthday attack

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 ...