same birthday

[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.