If the opposite of “at least” is “at most”, why is the complement of “at least two people share the same birthday” equal to “**no one shares the same birthday**” and not “at most two people share the same birthday?” Hi, welcome to Philosophy SE.

## What is the probability that among n people at least two have same birthday?

The chance that THEY have the same birthday is **1/365**.

## What is the probability that exactly 2 people have the same birthday?

In a room of just 23 people there’s a **50-50** chance of at least two people having the same birthday. In a room of 75 there’s a 99.9% chance of at least two people matching.

## How many people must be present to guarantee that a at least two have the same birthday?

By the pigeonhole principle, you would need to have **366 people** in a room in order to have a 100% chance (a guarantee) that at least 2 people share the same birthday (Note: for this workshop, we are assuming a 365-day year.

## How many individuals would you need in a group to ensure that there was at least 1 person who had an identical birthday?

The magic figure of **20** comes in – in fact it’s 23 – when the probability of having two people with the same birthday reaches 50/50. Put another way, if we selected many groups of 23 people we could be sure that half of the groups selected would contain two people with the same birthday.

## What is the probability that there are at least two people with the same birthday in a class of 40 students?

If there are 366 or more people, but only 365 possible birthdays disregarding leap year, then two or more of them must share a birthday.

Probability of Shared Birthdays. or, How to Win Money in Bar Bets.

Probability in a group of n people that 2 or more have the same birthday | |
---|---|

30 | 0.706 |

40 | 0.891 |

50 |
0.970 |

## What is the probability that at least 2 out of 5 people have the same birthday?

That is, about a **4%** chance that at least two of the six will have the same birthdays. It turns out that in a group of 23 people, there is slightly more than 50% probability that two people will have the same birthday, and for 50 people the probability becomes 97%, 60 people 99%.

## What is the probability of sharing a birthday?

While it may seem surprising that only 23 individuals are required to reach a **50%** probability of a shared birthday, this result is made more intuitive by considering that the comparisons of birthdays will be made between every possible pair of individuals.

Near matches.

k | n for d = 365 |
---|---|

5 |
8 |

6 |
7 |

7 |
7 |

## What is it called when you share the same birthday with someone?

**Birthday twins**. I have no citation, but have often heard this used to describe exactly what is asked: two or more, not necessarily related, born on the same day, regardless of year born. Other forms of the same construction are “astro twins,” “astrology twins,” and “star twins.”

## What do you call someone that shares the same birthday month?

However, it is usual in the English-speaking world to call people who share the same birthday as “**birthday twins**.” Less frequently “Irish twins,” especially in the sense of same day and month but one year apart.

## What are the chances of meeting someone with the same birthday and year?

7 Answers. Show activity on this post. For any one relationship, the odds of sharing the same month and day are approximately **1 in 365** (not exactly because of leap year and because births are not exactly evenly spaced within a year.

## What is the probability of two friends having their birthday on the same day in a leap year?

If both have same birthday, then it may be any of one day from 365 days. It means favourable case is one while total number of possible outcomes is 365. Hence, Probability of having same birthday = **1/365**.

## How many people share a birthday in room?

The birthday paradox – also known as the birthday problem – states that in a random group of 23 people, there is about a 50% chance that two people have the same birthday. **In a room of 75 there’s even a 99.9% chance of two people matching**.

## What is the rarest birthday?

**This Is the Least Common Birthday in the U.S. (No, It’s Not Leap Day)**

- February 29.
- July 5.
- May 26.
- December 31.
- April 13.
- December 23.
- April 1.
- November 28.

## What is it called when two siblings have the same birthday?

When people refer to **Irish twins**, it’s important to recognize that although the siblings are close in age, they are not actually twins. In other words, they were not born during the same gestational period. Calling them Irish twins is just an informal way of classifying siblings that are born close together.

## Is it rare for siblings to have the same birthday?

The random odds against five single siblings sharing a birthdate are **one in 17,797,577,730** – almost 4 times the world’s population.

## What is twin birthday?

“birthday twins” (**born on the same day & same month**) “birthdate twins” (born on the same day & same month & same year) “time twins” (born on the same day & same month & same year) btw. there is a similar website with people born on the same day (same date) – https://birthdays.astro-seek.com.