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Birthday paradox - Try this out

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Reply 160

mr96

21st October :smile:

Haven't seem my birthday buddy on here yet though I know some in real life!

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Reply 161

indigoblue265

Original post by yarshad

13th December ((((:

Mine too!

Reply 162

anna__

Original post by Artymess

12th of July :cute:

Birthday friend!!

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Reply 163

Jimbo1234

Ah, parents banging during the festive seasons. A story as old as time itself :biggrin:

1st June

14th November!

Original post by Anythingoo1

Wow you're very close to the leap year date (unless you weren't born in a leap year)

22nd of February here

I was born on 28th February and people always say to me 'oooh, you're lucky you weren't born a day later...' and I'm like, 'what's wrong with the 1st of March?'.

Reply 167

chapmouse

The paradox is that there is a wide assumption that there is always a 1 in 365 chance of people sharing a birthday. And so if you were to gather 57 people and open up bets on at least one pair of people sharing a birthday, you should always bet on it, because 99% of the time, it happens, and indeed it happened here.

The birthday paradox was taught to me as part of my Statistics module in AS Level maths, using it to understand Permutations.

The idea is to think about it as the amount of pairs of people can be made, and to remind yourself that each pair has a 1/365 chance of sharing the same birthday.

So here's the maths:
Assuming there are

57

people
and there are

365

days in a year (For simplicity, we ignore leap years and twins etc.)
The amount of pairs is found by

\dfrac{No. of People * (No. of People - 1)}{2} \rightarrow \dfrac{57*(56)}{2} = 1,596

The chance of All of the pairs having different birthdays is equal to

(1-\dfrac{1}{365})^no. of pairs = (\dfrac{364}{365})^1596= 0.0125428616[size="2"]23[/size] [br]and the chance of the pairs sharing the same birthday is equal to [latex]1-0.01254[/latex][br]which is[br][latex]0.987457[/latex][br]which, when displayed as a percentage is[br][latex]0.98746 * 100 = 98.7[/latex][size="4"]%[/size] or: [size="7"]99%[/size] to 2 sig figs.[br][br]Hopefully that is moderately clear maths, sorry if not!

(edited 11 years ago)

21st July

15th January

Haven't seen anyone with 26th June....anyone? :biggrin:

Reply 171

username306617

Original post by gomg

4th August

Snap!

25th February

1st January. My girlfriend's birthday is also 1st January.

Reply 174

Sannn

Hrm. 23 Feb is sure proving to be elusive... :colonhash:

Reply 175

M.M.HUSSAIN

Original post by Luxray

I have to say this paradox is quite intriguing
For the record I'm 23rd August

u were born on results day!

Reply 176

Anythingoo1

Original post by notchip

I was born on 28th February and people always say to me 'oooh, you're lucky you weren't born a day later...' and I'm like, 'what's wrong with the 1st of March?'.

Well, it is March :nooo:

Seriously though, I don't know why people would say that, I wouldn't personally if I met you, and there is nothing wrong with March as far as I can tell?

Reply 177

xxSherlockxx

6th December anyone? xx

Reply 178

username91207

Original post by shadowdweller

Also 12th April :tongue:

I know loads of people with your birthday!

Reply 179

notchip

Original post by Anythingoo1

Well, it is March :nooo:

Seriously though, I don't know why people would say that, I wouldn't personally if I met you, and there is nothing wrong with March as far as I can tell?

Nah, there's nothing wrong with March. I'm normally just being obtuse because they always assume I'd have been born in a leap year, when they'd have more chance of being wrong about that than they would right.