I know what you are saying, but none of them were born by C-section. They were all natural births. Still you can plan the beginning to get the end date sorta close, but as Pie said - that would mean there are 23+ thousand of them.
Either way its still kinda weird.

My dad, my son and I are all born on the 30th of different months. What are the odds of that?

You can also induce. And each generation has a dozen tries or so to get it right. If you make it a priority.

If it's random, then yeah, it's pretty unlikely. But if you were weird and made it a priority, you could pretty much nail it. Eventually.

The last child was not C-section, that much we know. The article doesn't say none of the rest of them were c-section, that I saw anyway.

So, Grandpa's son could've been c-section, then grandson was just close and they could have induced, or even drawn it out to make it fall on the right date.

I only say this because I was born on my dad's birthday. I was c-section.

The initial article and I were wrong....Updated info.

Well it's been a while since I took stats, but lets see if I can get it.

The odds of any one of you being born on a 30th is 12/365. Twelve 30ths in a year. 365 days in a year.

The odds of all of you being born on a 30th is the odds of each one multipled together so (12^3) / (365^3).

Pretty sure that's right.

Or perhaps you were being rhetorical.

There isn't a February 30th. :p:

Oops. Bound to get something wrong.


So that means singleton odds - 11/365.

All of them = (11^3) / (365^3).

For three generations on the same day, ignoring leap years, assuming random birth dates and one child per generation, I figure:

Grandpa born on any day = 1/1 chance, since it sets the day.

Father born on same day = 1/365.

Son also born on same day = another 1/365.

= (1/365)/365
= 1/133,225

If you require that all three are born on a specified date (eg May 8th) it is another 1/365 (for Grandpa to also be born on that date) which works out at 1 / 48,627,125.

I don't think the date can be set in advance, so I go for 1 / 133,225.

However, given that each generation has more than one child, and birth timings are not random, the real odds should be substantially lower. It's very hard to say, but allowing 3 children per generation and some tendency to deliberate seasonal breeding, I'd guess somewhere in the 1 / 30,000 to 50,000 range.

Really there must be scads of them.

In that case, I guess it isn't weird - I withdraw my post.

I was also trying to factor in the 50/50 split that each successive generation could have had a daughter and not a son -- and then the 2.2 children per 'average' family.

That got me closer to their number.

Okay, if you stipulate all three must be male, that narrows it down, but if you allow two children per generation that puts is back up. And in older generations the average number was higher.

My high school mate shares his birthday with his daughter.

I reckon Pie knows this already, but ... how many people do you think you would need in a group to give a 50% or more chance that two people share a birthday?

:3eye:
...waiting...

My birthday is the day after my mother's. The girl shares a birthday with her aunt. Jim shares a birthday with my sister's husband.

Don't look at me! I sux at maths. ;)