same birthday

[dark_horse]

my brother, my grandfather and i all have the same birthday.
please settle an age old family debate.

the odds of my brother and i having the same birthday is 365:1.
the odds of my brother and i being born on one particular date is 365x365?
the odds of the 3 of us having the same birthday is?
the odds of the 3 of us being born on one particular date is?

[SheetWise]

The math is straight forward, but I would focus more on the observation. For example, I have three daughters whose birthdays are the 24th, 25th, and 26th of the same month. The probability of this recurring would be the same. So would the recurrence of any three random dates. There are probably several other people in your family who are not a part of this apparent "convergence". I've attached a favorite observation from a great book -

[ QUOTE ]
The sample space of "unusual" events is confused with that of low-probability events. For one example, the remarkable feature of a bridge hand of 13 Spades is its apparent regularity, not its rarity (all hands are equally probable). For another, if one holds a number close to the winning number in a lottery, one tends to feel that a terribler bad stroke of misfortune has caused one just to miss the prize. Bertrand Russell's remark that we encounter a miracle every time we read the license number of a passing automobile is encompassed by this fallacy. The probability of an "unusual" occurrence should be equated to the ratio of the number of unusual (by virtue of symmetry or other aesthetic criteria) events to the total number of events.

[/ QUOTE ]

from The Theory of Gambling and Statistical Logic by Richard Epstein, Paranormal Phenomena - Fallacies and Sophistries;

[dark_horse]

so what are the odds dude

[SheetWise]

If I understand your question; I am left with -

3 of us having the same birthday;
3 of us being born on one particular date;

If you are incapable of the math, I doubt the time I spent exposing some of the subtleties helps you.

Strangely Symmmmettrically Atttaccched ...

[Nottom]

[ QUOTE ]
I have three daughters whose birthdays are the 24th, 25th, and 26th of the same month. The probability of this recurring would be the same.

[/ QUOTE ]

Any chance they are November babies?

[MikeL05]

[ QUOTE ]

the odds of the 3 of us having the same birthday is?
the odds of the 3 of us being born on one particular date is?

[/ QUOTE ]

heavily influenced by hindsight bias. How many brothers do you have? How many sisters? And how many brothers and sisters does your mom/dad (whoever is the child of the grandfather) have?

What you really want to do, is determine a given date of birth for your grandfather. Then determine the number of children he had, add 1 for you and add 1 for each brother/sister you have. Then figure the odds of two of you, out of whatever total number that is, have the same birthday as him.

[LetYouDown]

If I'm understanding your question correctly...

The odds of you and your brother having the same birthday are 364:1.
The odds of you and your brother being born on one particular date are 133224:1.
The odds of you all having the same birthday are 133224:1.
The odds of you all being born on one particular date are 48627124:1.

Remember there's a difference between odds and probability.

[dark_horse]

[ QUOTE ]
If I'm understanding your question correctly...

The odds of you and your brother having the same birthday are 364:1.
The odds of you and your brother being born on one particular date are 133224:1.
The odds of you all having the same birthday are 133224:1.
The odds of you all being born on one particular date are 48627124:1.

Remember there's a difference between odds and probability.

[/ QUOTE ]

Explain?

[LetYouDown]

[ QUOTE ]
The odds of you and your brother having the same birthday are 364:1.

[/ QUOTE ]
You have a birthday...doesn't matter what day. So the probability he has the same birthday is 1/365 or 364:1.

[ QUOTE ]
The odds of you and your brother being born on one particular date are 133224:1.

[/ QUOTE ]
The probability that either of you are born on June 16th is 1/365. The probability that both of you are born on June 16th is 1/365 * 1/365 or 1/133225 or 133224:1.

[ QUOTE ]
The odds of you all having the same birthday are 133224:1.

[/ QUOTE ]
You have a birthday...doesn't matter what day. The probability that your brother is born on the same day is 1/365. The probability that your grandfather is born on the same day is 1/365. So 1/365 * 1/365 = 1/133225 or 133224:1.

[ QUOTE ]
The odds of you all being born on one particular date are 48627124:1.

[/ QUOTE ]
The odds that you're all born on June 16th is 1/365 * 1/365 * 1/365 or 1/48627125 or 48627124:1.

Edit: Keep in mind, I'm assuming that you're really just looking for an answer here. All of the nuances discussed by others in this thread are valid. My numbers represent you picking three random people off the street.

[SheetWise]

[ QUOTE ]
Any chance they are November babies?

[/ QUOTE ]
How did you know?