How smart are you?

If there are 30 people in a room, what is the % chance that at least 2 people share a birthday?

• Less than 10%
• 10% to 25%
• 25% to 50%
• More than 50%

0 voters

If there are 30 people in a room, what is the % chance that at least 2 people share a birthday?

not very didn’t read the question properly

Problem not. Maybe answer question you did.

#^&### poll!!! :raspberry: #^^###@#%*! :fume:

Maybe I’m not smart enough. Can’t get the damned poll to work. Is there a solution?

366 possible dates depending on whether born in leap year.
so 30/366 gives about 12% for any given date
Assuming the year is not important
If it is actual birth day required then possible age ranges from 0 to say 100 would mean 0.12% right?

[quote=“Edgar Allen”]366 possible dates depending on whether born in leap year.
so 30/366 gives about 12% for any given date
Assuming the year is not important
If it is actual birth day required then possible age ranges from 0 to say 100 would mean 0.12% right?[/quote]

That also doesn’t account for seasonal adjustment which is always a factor in birthing rates.

I assumed an evenly spread geographical mix.

that depends on who’s buying, and who’s lying…

[quote=“Mother Theresa”]#^&### poll!!! :raspberry: #^^###@#%*! :fume:

Maybe I’m not smart enough. Can’t get the damned poll to work. Is there a solution?[/quote]

[quote=“Maoman”][color=#000040]
you CAN vote, you just have to go to your User Control Panel (top of the page) and switch your board style to prosilver. After you’ve voted, you can switch back to the Forumosa board style if you wish. It’s not an elegant solution, but it works as a temporary fix.

[/color][/quote]

Prosilver is an evil cult,

May be, and it sure is ugly, but I’m thrilled that I was one of only 3 people smart enough to follow Maoman’s instructions (posted by jimi) to cast my vote. :discodance:

Anyway, I saw this poll on linkedin this morning and it tricked me so I thought I’d place it here.

Edgar Allen, I initially thought something like what you said, but apparently that’s wrong. According to the wikipedia article alidarbac linked to above. . . .

Weird, huh?

What tricked you is that you’re thinking of the probability one person will have a particular birthday, but that’s not the issue. There are actually a few hundred possible pairings that would solve the problem.

If there are 30 people in a room, what is the % chance that at least 2 people share a birthday?

Less than 10%
10% to 25%
25% to 50%
More than 50%

No idea. My math sucks. But just thinking it through, I imagine that for person A, who has a given birthday, there is on average a roughly 1/356.25 chance that each other person in the room (numbering 30-A = 29) has that same birthday, which chances total 29 x 1/356.25, or 0.08140350877192982456140350877193 for that person A’s birthday. The same chance exists for person B, except that I think you have to subtract one from the number of other persons since the chance for sharing a birthday with person A has already been counted. So for B the chance of a birthday shared with anyone other than A is 28 x 1/356.25 or 0.076659822039698836413415468856947. Continuing on, subtracting one more number from the number of remaining persons each time, and then adding the results for the first 29 people (the 30th has already been factored into the prior 29 calculations), we get 1.190965092, which is odd, since it’s higher than 1 (100%). So I picked over 50%.

Am I close?

The scientists will try to tell you that the probability is real high. But my ‘feelings’ tell me that they are wrong. I don’t know why they are perpetrating this hoax. Just to make themselves ‘feel’ superior I suppose.

Very basic maths. But the poll thing? Meh.

I got another one…

You appear on the game show. You are shown three doors, behind one is the prize.

You first select one door. The host then always opens one of the two remaining doors and he always shows you a door which does not have the prize. He then asks you whether you want to switch your choice to the other remaining door, or stick with your original choice.

What do you do?

Change. That one’s in ‘The Curious Incident of the Dog In the Nighttime’ by Mark Haddon.

Congrats, you win a prize. Well, two-thirds of the time you do

Anyway - it’s been shown that children who have not been taught any probability theory are more likely to choose switching than those who have. Similarly, pigeons seem to be very good at choosing to switch doors when given the opportunity to do so.

It’s an instance where people’s innate intuition is stymied by education.

I love that section of the book because the point the kid is trying to make is that ‘logic’ isn’t logical, and that most people are too stupid to know that their ‘common sense’ is wrong.

Here’s another mindbender posed by a guy in my office: ‘Why do chicks eat so many bananas?’