Wednesday Puzzle

[jamief]

No looking this up please!

Given a group of people, what is the minimum group size you need to be almost (i.e. 99% certain) that a pair within the group will share the same Birthday?

 

[PardonTheWait]

50

 

[Steeps]

366 not taking into account leapyears.

 

[jamief]

Not quite! I see you've encountered this "problem" before

 

[jamief]

366 not taking into account leapyears.

Nopes

 

[Wang]

367, assuming someone is born on February 29th. I'm expecting to be told i'm totally wrong though and made to look a total ass

 

[camels5]

366 not taking into account leapyears.

 

[BlastRadius]

2

Just make sure they are twins

 

[jamief]

Its not 364,365,366 or 367 (or anything close!)

You'd be surprised

 

[Zogger]

20ish

 

[Gilly]

As it is any of the group sharing, not any of the group sharing with me, I'd go with about 25-30.

 

[Wang]

Its not 364,365,366 or 367 (or anything close!)

You'd be surprised

You are right, i am surprised.

 

[camels5]

64

 

[Aero]

2

Just make sure they are twins

I agree

 

[jamief]

The correct answer is 56

It can be quite a complex problem to understand, but see http://en.wikipedia.org/wiki/Birthday_problem (the Understanding the problem bit), quite interesting too. I stumbled upon it doing some programming research

 

[Brownpants]

one?

 

[Yeggstry]

Well I know that its 23 for 50% (no I didn't look it up, I remembered it from school).

Not sure about the almost certain, though 50 sounds about right.

 

[div0]

About 60

 

[MookJong]

My first thought was twins, I dunno how many births you have to have to get a set of twins but it would be that amount. So if twins are 1 in every 150 births the answer would be 150.

Two people in my class at school had the same Birthday so it could be 30 lol.

EDIT...oh I see

 

[PurpleDinosaur]

It's only something you really want to "understand" if you enjoy maths.