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# Birthday paradox - Try this out Watch

1. 21st October
Haven't seem my birthday buddy on here yet though I know some in real life!

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13th December ((((:
Mine too!
3. (Original post by Artymess)
12th of July
Birthday friend!!

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4. Ah, parents banging during the festive seasons. A story as old as time itself
5. 1st June
6. 14th November!
7. (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?'.
8. 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 people
and there are days in a year (For simplicity, we ignore leap years and twins etc.)
The amount of pairs is found by
The chance of All of the pairs having different birthdays is equal to
and the chance of the pairs sharing the same birthday is equal to
which is

which, when displayed as a percentage is
% or: 99% to 2 sig figs.

Hopefully that is moderately clear maths, sorry if not!
9. 21st July
10. 15th January
11. Haven't seen anyone with 26th June....anyone?
12. (Original post by gomg)
4th August
Snap!
13. 25th February
14. 1st January. My girlfriend's birthday is also 1st January.
15. Hrm. 23 Feb is sure proving to be elusive...
16. (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!
17. (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

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?
18. 6th December anyone? xx
Also 12th April
20. (Original post by Anythingoo1)
Well, it is March

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.

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Updated: June 9, 2017
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