# Questions tagged [birthday]

Birthday problems typically look at probabilities and expectations of a random group of individuals sharing birthdays and how this changes as the number of people increase. They often assume that individuals' birthdays are independently uniformly distributed across 365 days but similar problems can use other numbers or assumptions. They can be generalised to wider occupancy and collision problems.

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### What is the probability that three living people in the same family will celebrate their birthdays on exactly the same day.

I celebrate my birthday on the same day as one of my grandchildren. Just wonder how rare it would be for three people in the same family to celebrate their birthdays on the same day.
1 vote
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### Progressive Birthday problem

The Birthday Problem is very interesting to me. The more dates you fill up, the lower the chances a date will be outside what has already been seen. But I do not seem to understand at all how ...
1 vote
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1 vote
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### Birthday problem but with $2^{128}$ different days in the year [duplicate]

I am trying to calculate how many randomly generated ids I need to produce for there to be a 1% probability I get a duplicate id. There are $2^{128}$ possible ids. I understand this is just the ...
1 vote
115 views

### What is the probability that with 100 people, there are 3 consecutive birthdays at some point in the year?

Assumptions: $365$ days in the year. All birthdays are equally likely. The three consecutive days must fall within the same calendar year. This was a fun problem that came up at my office of $100$ ...
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1 vote
235 views

### Expected number of aces in a poker hand

So I'm having difficulty understanding a certain idea. Say I have a standard $52$ card deck (fairly shuffled, etc.) and I pull $5$ cards from it. We ask, what is the expected value of the number of ...
116 views

### Using R, solve the birthday paradox

The probability that two students in a class have the same birthday is at least 75%. What is the minimum size of the class? I tried, ...
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1 vote
75 views

### Probability of 4 parents sharing 2 birthdays [closed]

I'm a math idiot and I'm trying to figure something out. My mother was born on April 10th as was my friend's mother. My father was born on July 4th as was my friend's father. How do I calculate the ...
• 21
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### My try of the Birthday Paradox

I have seen the solution of the paradox on Wikipedia, but before that I tried it out myself. But I got my answer wrong with my approach. To calculate the probability of no two people in a group of 23 ...
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