Holmes today

[BaaLocks]

14 hours ago, Inverurie Ram said:

Duane will guide us home...........sing up!

@2tupsand @Inverurie Ram will be at Martin Stephenson & The Daintees at the Derby Venue on Fri 9th Nov 2018.

Who's coming to join us?

 

Going to see him the night before at the Hare & Hounds in Brum - I'll ask him to keep some in the tank for you

[Carl Sagan]

As the thread is "Holmes Today" I thought I'd post Happy Birthday, Duane! 

And it's also Bryson's birthday today, so Happy Birthday, Craig! 

A fabulous example of what mathematicians call "the birthday problem". In a group of 23 people it's more likely than not that two will share a birthday.

[Ghost of Clough]

5 hours ago, Carl Sagan said:

As the thread is "Holmes Today" I thought I'd post Happy Birthday, Duane! 

And it's also Bryson's birthday today, so Happy Birthday, Craig! 

A fabulous example of what mathematicians call "the birthday problem". In a group of 23 people it's more likely than not that two will share a birthday.

Isn’t it just as likely?

[Carl Sagan]

24 minutes ago, Ghost of Clough said:

Isn’t it just as likely?

No - the probability is just over 0.5. If ignoring leap years, once you have 23 people it's 0.5073 that two will share a birthday, versus 0.4927 that no two birthdays wil be the same.

[richinspain]

33 minutes ago, Carl Sagan said:

No - the probability is just over 0.5. If ignoring leap years, once you have 23 people it's 0.5073 that two will share a birthday, versus 0.4927 that no two birthdays wil be the same.

Although I've heard this before, I don't get it. So 23 people together, that's 23 possible days out of 365! Why is it so likely that 2 coincide?

[Millenniumram]

1 hour ago, richinspain said:

Although I've heard this before, I don't get it. So 23 people together, that's 23 possible days out of 365! Why is it so likely that 2 coincide?

To do with combinatorics if I recall, I’d explain it but I’m rubbish at that area, even as a maths student...

[Carl Sagan]

2 hours ago, richinspain said:

Although I've heard this before, I don't get it. So 23 people together, that's 23 possible days out of 365! Why is it so likely that 2 coincide?

It's because you're saying two will share, but you're not specifying the day. Person one has a choice of 365 out of 365 days. So as not to coincide, person two can only have a birthday on 364 out of 365 days. Person three is then 363 out of 365. So with three people the odds of them not sharing a birthday are (365 x 364 x 363)/(365 x 365 x 365). By the time you get to 23, that figure falls below half (to the 0.4927 I mentioned). Hope that makes sense?

[Parsnip]

365/23 = 16. So Scott Carson has a 1 in 16 chance of sharing his birthday with another squad member. Same applies to everyone so that's 23 chances of hitting a 1 in 16 shot. So yeah, more than likely.

Is that it? Do I get it?

[richinspain]

27 minutes ago, Carl Sagan said:

It's because you're saying two will share, but you're not specifying the day. Person one has a choice of 365 out of 365 days. So as not to coincide, person two can only have a birthday on 364 out of 365 days. Person three is then 363 out of 365. So with three people the odds of them not sharing a birthday are (365 x 364 x 363)/(365 x 365 x 365). By the time you get to 23, that figure falls below half (to the 0.4927 I mentioned). Hope that makes sense?

Thanks for explaining it, but it still doesn't make sense to me. Although I know several groups of friends and family who share birthdays I'm talking about hundreds of people. What really surprises me though is that in my job I see literally thousands of identity cards each year, and I think in my 13 years doing the job I have only seen a couple of people who share my birthday (6th of June, who for example on here shares my birthday?).

[Carl Sagan]

2 minutes ago, richinspain said:

Thanks for explaining it, but it still doesn't make sense to me. Although I know several groups of friends and family who share birthdays I'm talking about hundreds of people. What really surprises me though is that in my job I see literally thousands of identity cards each year, and I think in my 13 years doing the job I have only seen a couple of people who share my birthday (6th of June, who for example on here shares my birthday?).

That's why its counterintuitive. Someone has a 1/365 chance of sharing YOUR birthday, or a 364/365 chance of them not. Th 23 number is the better than even chance of any two in the group sharing a birthday.

The forum doesn't allow for mathematical formatting and expressions, so it's difficult to write out the workings. You might think having 183 other people in the room would give a better than even chance of another person sharing yours, but that's not the case because all their birthdays fon't have to be on different days. So we take (364/365) annd raise it to the nth power and when that falls below 0.5 we have the number we're after. That number is 253.

This means you'd need 253 other people in the room for it to be more ikely than not that one will share your birthday.

I feel I've not explained that very well!

[WystonRam]

12 minutes ago, Carl Sagan said:

That's why its counterintuitive. Someone has a 1/365 chance of sharing YOUR birthday, or a 364/365 chance of them not. Th 23 number is the better than even chance of any two in the group sharing a birthday.

The forum doesn't allow for mathematical formatting and expressions, so it's difficult to write out the workings. You might think having 183 other people in the room would give a better than even chance of another person sharing yours, but that's not the case because all their birthdays fon't have to be on different days. So we take (364/365) annd raise it to the nth power and when that falls below 0.5 we have the number we're after. That number is 253.

This means you'd need 253 other people in the room for it to be more ikely than not that one will share your birthday.

I feel I've not explained that very well!

I thought he played well especially as it was just before his birthday. 

[Parsnip]

So I don't get it?

[Carl Sagan]

51 minutes ago, Parsnip said:

So I don't get it?

Sadly not. But I was guessing you knew that. Damn fine attempt though. 

[Parsnip]

33 minutes ago, Carl Sagan said:

Sadly not. But I was guessing you knew that. Damn fine attempt though. 

[Igorwasking]

This was not a thread I needed to read at 6.41 in the morning. My head hurts!

Oh, and it’s Mrs Igor’s birthday today! ? 

[archram]

9 hours ago, richinspain said:

Thanks for explaining it, but it still doesn't make sense to me. Although I know several groups of friends and family who share birthdays I'm talking about hundreds of people. What really surprises me though is that in my job I see literally thousands of identity cards each year, and I think in my 13 years doing the job I have only seen a couple of people who share my birthday (6th of June, who for example on here shares my birthday?).

My eldest son was born on 6/6/66

[SuperFrankieL]

Little late to the topic but Carl's first reply is a solid explanation. If you want a bit of extra convincing, here is a good link.

[richinspain]

2 hours ago, archram said:

My eldest son was born on 6/6/66

My birthday is 6/6/63, and my sister 3/6/66

[The Scarlet Pimpernel]

2 hours ago, SuperFrankieL said:

Little late to the topic but Carl's first reply is a solid explanation. If you want a bit of extra convincing, here is a good link.

Emmmm………..Obviously quite a smart cookie...………..No wonder you are morphing into a Ram! ?

[richinspain]

2 hours ago, SuperFrankieL said:

Little late to the topic but Carl's first reply is a solid explanation. If you want a bit of extra convincing, here is a good link.

It still does my head in, but I at least understand how it works now. Thanks for the excellent explanation.