Probability of 2 individuals sharing same birthday and death My daughter died a year ago, my friends daughter died exactly 1 yr. later. I discovered at the funeral that both also shared the same birthday. What is the probability of the occurance that they shared the same dob and dod and that they both died of unknown causes? (in most simple terms please-if at all possibel!) Thank you!
 A: I'm sorry for the losses that you and your friend have had to experience.
As for the probabilities, we have that the probability that any two people share the same birthday is $1/365$ (ignoring February 29). The first person could have been born any day of the year and the second person has exactly one day out of the $365$ to have been born on in order to match him/her.
Similarly, the probability that they share the same date of departure is $1/365$
So the probability that the D.O.B. and D.O.D are shared would be the product of these two: $\frac{1}{365^2} \approx .0000075$
As far as the last part goes (both dying of unknown causes) this isn't really possible to consider  unless we happen to know the probability of dying of an unknown cause in general.
A: Sorry for your loss. I was hesitant before answering.
Indeed there are 365 pairs of matching bod: $(1,1),(2,2),\dots,(365,365)$. There are $365^2$ possible pairs of bod.
Assume the dob are uniformly distributed. Dob match for 2 people with probability: $\dfrac{365}{365^2} = \dfrac{1}{365} \approx 3 \mathrm{\ chances \ out \ of \ } 1000$.
Likewise, the probabilities of matching dod is $\approx 3 \mathrm{\ chances \ out \ of \ } 1000$. 
If the two events are independent you can multiply the probability and get $\approx 1 \mathrm{\ chance \ out \ of \ } 100,000$ of matching dob and dob.
In reality, both dob and dod are not at all uniformly distributed because the "conception" dates are not. On a national level you are more likely to be conceived during national holidays for example. I would expect the probability of matching dob to be even higher within the same group of friend.
