Odds of this strange coincidence
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Odds of this strange coincidence

[From: ] [author: ] [Date: 12-06-16] [Hit: ]
Ignoring the leap year issue, a dead person has a 2/365 chance of one of those events being on 20th April (and a 1/(365^2) chance of both, and a live person has a 1/365 chance of having been born on that date.Similarly, a dead person has a 363/365 chance of NOT having that date feature, and a live person 364/365.......
What are the odds of this happening?

A sequential number of cards numbered 1 to 365. Eight people draw a card.

Of those Eight people four of them draw exactly the same card.

Reason behind this is my family of 8 people has a strange coincidence.

Four of the members of my family have either died or born on April 20th (different years of course)

Now I can figure that one dieing and on being born is 364:1 (depending on if its a leap year or not)

-
We need to take into account that you are counting both birth and death - ie 2 events per person (or 1 for those still alive).
Ignoring the leap year issue, a dead person has a 2/365 chance of one of those events being on 20th April (and a 1/(365^2) chance of both, and a live person has a 1/365 chance of having been born on that date.
Similarly, a dead person has a 363/365 chance of NOT having that date feature, and a live person 364/365.

The total probability of exactly 4 of the 8 depend on how may of your 8 family members are still alive.
For each person, look at the odds of what happened and multiply all 8 probabilities together. For example, if you are counting only 2 dead people, one of whom died one that date and the other who was neither born nor died on the date, the total probability would be
(1/365)^3... for the 3 birthdays of live people
x
2/365 ... for the person who died on 20th April
x
363/365 ... for the person who died and was born on some other date
x
(364/365)^3... for the 3 living people with other birthdays
= 264,264/365^8 = 8*10^-16 or less than 1 in 100,000,000,000,000

spooky!
1
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