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9 replies to this topic

### #1 qedmike

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Posted 10 November 2008 - 10:49 PM

There are one hundred double-sided coins on a table, 30 have the tails side facing up and 70 have the heads side facing up. You are blind folded and brought to the table. You must create two separate piles that contain the same number of 'tails up' coins (in other words, the two piles you create must contain the same number of tails facing upward). You are not able to 'feel' to see if a coin is heads up or tails up.

How can this be done?
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### #2 clozobozo

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Posted 10 November 2008 - 10:52 PM

Spoiler for probably not correct..

i have no idea... <_<
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### #3 Lost in space

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Posted 10 November 2008 - 11:04 PM

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### #4 Prime

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Posted 10 November 2008 - 11:22 PM

I understood, the two piles do not need to have the same number of coins, just the same number of tails.
Spoiler for Solution

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Past prime, actually.

### #5 Lost in space

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Posted 10 November 2008 - 11:26 PM

I understood, the two piles do not need to have the same number of coins, just the same number of tails.

Spoiler for Solution

And you do this blindfolded, also the coins are not in piles to start with ???
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### #6 Prime

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Posted 10 November 2008 - 11:31 PM

And you do this blindfolded, also the coins are not in piles to start with ???

Is that difficult?
Spoiler for method

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Past prime, actually.

### #7 Lost in space

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Posted 10 November 2008 - 11:38 PM

Is that difficult?

Spoiler for method

Are the coins random or not??
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### #8 qedmike

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Posted 11 November 2008 - 12:08 AM

Prime got it right.

Lostinspace, it is random, but it doesn't matter.
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### #9 Blonde Girl

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Posted 12 November 2008 - 12:20 PM

omg .... i can't believe that works... now I am going to have to go and try it myself!!!!
mmm one small problem I don't have that many coins!

hehehe
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### #10 Prime

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Posted 12 November 2008 - 07:47 PM

omg .... i can't believe that works... now I am going to have to go and try it myself!!!!
mmm one small problem I don't have that many coins!

hehehe

You don't need actual coins to test that solution. Just imagine you set aside 30 coins. Then choose any number between 0 and 30. Say, you picked number 5. Now assume there are 5 tails among 30 coins set aside. Then there are 25 tails remaining in the other pile. There are also 25 heads in the 30-coin pile that you set aside. When you turn over every coin from the 30 set aside, you get 25 tails and 5 heads. Now recall, there are also 25 tails in the other pile.
Repeat this exercise for every number of tails in the 30-coin pile between 0 and 30.
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Past prime, actually.

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