What is the probability of both Grandmothers dying on the same day, but 10 years apart?

Question

Not seeing my Mother's side of the family since I was 11, I didn't know when my Grandmother passed. Fast forward to June 29th, 2019, my Father's mother passed. I found my maternal grandmother's obituary online in 2021, and when I seen the date she died I couldn't belive my eyes. My maternal grandmother passed away June 29th, 2009. My paternal grandmother passed away June 29th, 2019. I mean what are the odds????

Answer 1

This is similar to the question: if you have 30 friends, what is the probability that two of them have the same birthday? It turns out the odds are about 71%, and this is a well-known finding.

So, if you have 30 acquaintances or more (friends, relatives, co-workers, etc.), such an event is quite likely. Not 1/365, by the way. But it seems so unusual that we ignore all the times that this was not the case.

Answer 2

It's reasonable to assume that it is equally likely for death to occur on any day of the year. We can boil this question down to what is the probability your paternal grandmother passed away June 29th. That probability is 1/365 (1/366 in a leap year).