Did you know

A bat is the only animal that flies
In world war 1 the south african army had a private called Jackie who was a baboon.
A pineapple is a berry
Pigs get sunburned
In a room of just 23 people there is a 50% chance that 2 of them will share a birthday

 

No, I did not.

 

So, in a room of 46 people, is there a 100% chance that 2 people will share a birthday. If not please explain. 100% of statistics are wrong. That is particularly true of the statistics produced on here.

 

No in a room of 23 people there is a 50% chance, in a room of 57 people it's a 99% chance and for 100% you need 367 people. Google it to read more about how it works, it's quite complicated but quite simple once you've read it. I think it's called the birthday problem.

 

A fly is an animal. A bird is an animal. I'm guessing you mean mammal, but even then you're on shaky ground.


http://en.wikipedia.org/wiki/Flying_and_gliding_animals

 

FYI Birds are animals

sithi

 

That obviously isn't how probability works. If you flip a coin there's a 50% chance it will be heads. If you flip 2 coins there isn't a 100% chance of one of them being heads.

HH
HT
TH
TT

There's a 3 in 4 or 75% chance.

 

Fiddlesticks. yes I did mean mammal. Why is it shaky ground? I was only repeating what I'd heard so if it's wrong i'd be interested on why.

 

Re: FYI Birds are animals

Animal, mammal. They sound similar if you're stupid like me.

 

Depends on your definition of flight. Lots of animals glide. Flying squirrels for instance.

 

Valid point. If I jumped out of a tree and glided (is that even the correct past tense or is it glode or something?) I think i'd be telling everyone I could fly.

 

For those of to that are interested, it was a problem we briefly looked at in my first year at uni.

Rather than attempting to find the probability that two people share the same birthday you must consider the probability that none do.
P(None share a birthday) = 1 - P(A birthday is shared)

To work out the probability that none share a birthday you must consider each person in turn in compare them to each previously considered person.

If we begin with the first person, the probability that they have a different birthday to all previously considered people is 1 or 365/365 since this is the first person we have looked at.

The second person has a 364/365 chance of having a different birthday since there is just one day that has currently been taken.

The third person had a 363/365, the fourth has a 362/365 and so on until the 23rd has a 343/365 chance.

For none of the people to share a birthday we need all of these to occur. Since they are independent we can just multiply them together.
(365/365)x(364/365)x ... x(343/365) = 0.5 approximately.

Therefore if there is a half chance that none share the same birthday, there is a 1-0.5=0.5 chance that someone will.

 

thats just what i was thinking.

 

I bet you wish you'd never started this thread don't ya supertyke 

 

I think that in Supertyke's example, he must have used a 366 day year as it is not 100% until the 367th person. Nevertheless, that is the only statistic that is not counter-intuitive. I demand that the whole BBS goes into the same room so that we can check whether the statistics are born out by fact. Also, I would like to know how a power failure on the evening of 15 November, meaning no TV, video or BBS would affect the statistics.

 

Yeah he would have. It can be difficult to get your head around but doubling the number of people doesn't double the probability of something occurring.
Just as with the heads tails example, doubling the number of coins doesn't double the probability of getting a head.
The probability of getting a head with 1 coin is 1/2 (H but not T)
The probability of getting a head with 2 coins is 3/4 (HH TH HT but not TT)
3 coins is 7/8 (HHH HTT HHT THH THT TTH HTH but not TTT)
4 coins is 15/16
5 coins is 31/32
and so on.

Exactly like the Birthdays problem you're simply calculating the probability of it not occurring and taking it away from one. In this case it is 1 minus the probability of getting 1 tail with 1 coin, 2 tails with 2 coins, 3 tails with 3 coins etc:
T 1-1/2 = 1/2
TT 1-1/4 = 3/4
TTT 1-1/8 = 7/8
TTTT 1-1/16 = 15/16
TTTTT 1-1/32 = 31/32

Of course this means that while the probability will tend to 1 it will never actually reach or exceed it.

 

The chances of me getting head tonight is fecking zero

 

There is a 1 into 1 chance that Supertyke will find his own foot in his mouth with every post. If I had a hat, I would eat it. Supertyke needs a girlfriend, did you know?

 

I am pretty certain that the only animals that never fly are the larger whales and dinosaurs. Pterosaurs excepted, who had wings and flew frequently, I believe.

 

Depends where you toss the coin and where it lands.For instance if you was stood outside on a muddy field there is a chance that the coin will neither land on a head or a tail but on its side at a 90 degree angle.