### Brain Teasers

# Crowd

Probability
Probability puzzles require you to weigh all the possibilities and pick the most likely outcome.

14,500 people are sitting in a stadium. One of them is picked out. What are the chances that that person's birthday is on a Sunday?

### Answer

1/7. The number of people in the crowd is irrelevant.Hide Answer Show Answer

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## Comments

This has one foot in the "trick" section. Nice job.

This one is fun, yet quite easy, for an early morning crowd. If you want to enjoy a quick math and probability problem, this one will kick your day into gear. Wonderful teaser!

You almost got me! Fun teaser!

TRICKY!

I loved this one! Geesh - if ya don't get it right away - then ya want to kick yourself! - it's easy - but if you think too hard - da!

Yay! I said the answer to myself, thinking, no, I must have missed something, but NO! Being simple made me get one right! Yay!

This is one of my favourite types of problems. Thanks.

That all depends on what type of stadium the person what sitting in and what day he was sitting in it. Think about it.

that was way to easy, good simple one though

How would the amount of people in the crowd be irrelevant? :S

Because the other people in the crowd have no effect on this particular person's birthday being on any particular day.

that was nice

Say its football stadium on sunday and its a birthday special. Everyone with id gets in for free if their birthday ws a sun. That woudl change the odds. Otherwise its 6:1 against probability and 50 50 chances. Because it eiher is or isnt and the other six days dont matter.

Cool

I'd say 1 in 7 is the best possible probablity you could arrive at given the information at hand. This is based on the following two assumptions:

1. The birthday's of the crowd are spread evenly throughout the year.

2. That the current year is not known.

As has been pointed out the makeup of the crowd is very important, to get an accurate probability you'd have to know how many people in the crowd have birthdays on a sunday. Assuming that there is no special reason why the people born on Sundays would be more or less likely to be in the stadium then we'd be stuck with this assumption - while it is a fair assumption that doesn't necessarily make it right.

However, why on earthy wouldn't you know what the year was?! If we are to go with our first assumption that the birthdays are spread evenly then in 2006 (when the question is written) the chances of somebody having a birthday on a Sunday would be slightly higher than 1 in 7, whereas now (2007) the chances would be slightly lower.

For 2006 the chances would be 53 in 365 whereas in 2007 the chances would be 52 in 365. Next year (200 the chances would be the lowest (52 in 366).

1. The birthday's of the crowd are spread evenly throughout the year.

2. That the current year is not known.

As has been pointed out the makeup of the crowd is very important, to get an accurate probability you'd have to know how many people in the crowd have birthdays on a sunday. Assuming that there is no special reason why the people born on Sundays would be more or less likely to be in the stadium then we'd be stuck with this assumption - while it is a fair assumption that doesn't necessarily make it right.

However, why on earthy wouldn't you know what the year was?! If we are to go with our first assumption that the birthdays are spread evenly then in 2006 (when the question is written) the chances of somebody having a birthday on a Sunday would be slightly higher than 1 in 7, whereas now (2007) the chances would be slightly lower.

For 2006 the chances would be 53 in 365 whereas in 2007 the chances would be 52 in 365. Next year (200 the chances would be the lowest (52 in 366).

Read [2008] not (200

Pretty simple.

Just don't answer too quickly.

In fact,scratch that. Answer quickly and there's more chance you will et it right

Just don't answer too quickly.

In fact,scratch that. Answer quickly and there's more chance you will et it right

The answer is 1.

Since it doesn't say which year the birthday is in, the probability that the person has a birthday on a Sunday is 100%. You just need to pick the correct year.

Since it doesn't say which year the birthday is in, the probability that the person has a birthday on a Sunday is 100%. You just need to pick the correct year.

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