Our server costs ~$56 per month to run. Please consider donating or becoming a Patron to help keep the site running. Help us gain new members by following us on Twitter and liking our page on Facebook!
Current time: March 29, 2024, 4:02 am

Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Balls & Urns
#1
Balls & Urns
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:

Reply
#2
RE: Balls & Urns
You lost me at blue balls.
Reply
#3
RE: Balls & Urns
Sounds like a bicycle accident to me.
"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
Reply
#4
RE: Balls & Urns
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.
[Image: mybannerglitter06eee094.gif]
If you're not supposed to ride faster than your guardian angel can fly then mine had better get a bloody SR-71.
Reply
#5
RE: Balls & Urns
(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...
Reply
#6
RE: Balls & Urns
(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
"The Universe is run by the complex interweaving of three elements: energy, matter, and enlightened self-interest." G'Kar-B5
Reply
#7
RE: Balls & Urns
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
Reply
#8
RE: Balls & Urns
This isn't a lateral thinking problem! Stop thinking outside the box (or urn in this case)...

This is probability!

XD
Reply
#9
RE: Balls & Urns
(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
"The Universe is run by the complex interweaving of three elements: energy, matter, and enlightened self-interest." G'Kar-B5
Reply
#10
RE: Balls & Urns
(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
[Image: mybannerglitter06eee094.gif]
If you're not supposed to ride faster than your guardian angel can fly then mine had better get a bloody SR-71.
Reply





Users browsing this thread: 1 Guest(s)