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Atheist Forums › Science › Mathematics v
Balls & Urns

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Balls & Urns
Tiberius Offline
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#1
Balls & Urns
June 17, 2010 at 10:56 pm
An easy one for you today Big Grin

You have 101 coloured balls. There are 51 red balls and 50 blue balls.

You have two urns and have to put all of the balls into these. You can split them up any way that you want.

Now your friend has to pick one urn at random, put his hand in and choose one of the balls it contains (without looking!)

How should you have split the balls between the urns to maximize the chance that he will pick a red ball?

Answer:

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Shell B Offline
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#2
RE: Balls & Urns
June 18, 2010 at 10:53 am
You lost me at blue balls.
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Purple Rabbit Offline
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#3
RE: Balls & Urns
June 19, 2010 at 4:27 am
Sounds like a bicycle accident to me.
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Zen Badger Offline
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#4
RE: Balls & Urns
June 19, 2010 at 5:11 am
The alternative is to split the reds into 2 piles and the blues into 2 piles.

Put the 2 piles of blue balls into the urns and then put the reds on top.

Your friend is likely to only take a ball from the top.
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Tiberius Offline
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#5
RE: Balls & Urns
June 19, 2010 at 5:30 am
(June 19, 2010 at 5:11 am)Zen Badger Wrote: Your friend is likely to only take a ball from the top.
Make no assumptions in probability! If your friend always picks from the bottom of the urn, your method would get a blue ball every time...
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KichigaiNeko Away
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#6
RE: Balls & Urns
June 19, 2010 at 5:42 am
(June 19, 2010 at 5:30 am)Tiberius Wrote:
(June 19, 2010 at 5:11 am)Zen Badger Wrote: Your friend is likely to only take a ball from the top.
Make no assumptions in probability! If your friend always picks from the bottom of the urn, your method would get a blue ball every time...

Awww neda mind ZB

No cookie dis time! Sad
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Purple Rabbit Offline
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#7
RE: Balls & Urns
June 19, 2010 at 5:43 am (This post was last modified: June 19, 2010 at 5:45 am by Purple Rabbit.)
Just glue all blue balls together and to the bottom of the urn in one big chunk and you've fixed that problem.
Or get some decent red paint.
"I'm like a rabbit suddenly trapped, in the blinding headlights of vacuous crap" - Tim Minchin in "Storm"
Christianity is perfect bullshit, christians are not - Purple Rabbit, honouring CS Lewis
Faith is illogical - fr0d0
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Tiberius Offline
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#8
RE: Balls & Urns
June 19, 2010 at 5:46 am
This isn't a lateral thinking problem! Stop thinking outside the box (or urn in this case)...

This is probability!

XD
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KichigaiNeko Away
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#9
RE: Balls & Urns
June 19, 2010 at 5:47 am
(June 19, 2010 at 5:46 am)Tiberius Wrote: This isn't a lateral thinking problem! Stop thinking outside the box (or urn in this case)...

This is probability!

XD

ROFLOL

How else is an atheist to think???

Sorry Adrian but this one has me stumpedWorship
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Zen Badger Offline
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#10
RE: Balls & Urns
June 19, 2010 at 7:08 am
(June 19, 2010 at 5:46 am)Tiberius Wrote: This isn't a lateral thinking problem! Stop thinking outside the box (or urn in this case)...

This is probability!

XD

And the probability is that your friend will take it from the topCool Shades
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If you're not supposed to ride faster than your guardian angel can fly then mine had better get a bloody SR-71.
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Balls & Urns



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