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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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Posted · Report post

:lol:

yell at someone to do it for you!

i have no idea... <_<

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Posted · Report post

Make two piles of none??

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Posted · Report post

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

Divide coins into 70-coin pile and 30-coin pile. Then flip all coins in the 30-coin pile. Now the number of tails in the two piles is the same.

Explanation:

If x tails got into the 30-coin pile, then there are 30 - x heads in the 30-coin pile and 30 - x tails in the 70-coin pile. After flipping all coins in the 30-coin pile, the 30 - x heads became tails (same number as in the other pile), while x tails became heads.

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Posted · Report post

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

Divide coins into 70-coin pile and 30-coin pile. Then flip all coins in the 30-coin pile. Now the number of tails in the two piles is the same.

Explanation:

If x tails got into the 30-coin pile, then there are 30 - x heads in the 30-coin pile and 30 - x tails in the 70-coin pile. After flipping all coins in the 30-coin pile, the 30 - x heads became tails (same number as in the other pile), while x tails became heads.

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

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

Is that difficult?

Just shove all coins to the left side of the table. Then pick coins one by one flipping them over and moving them to the right, until you counted 30.

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Posted · Report post

Is that difficult?

Just shove all coins to the left side of the table. Then pick coins one by one flipping them over and moving them to the right, until you counted 30.

Are the coins random or not??

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Posted · Report post

Prime got it right.

Pick thirty coins from the pile and flip them over, separating them into their own pile. You now have the same number of tails in each pile.

When you pick a heads, there is the inverse tails in the other pile. The same is true when you pick a tails, there is an inverse heads. To cancel out the inverse effect, flip each coin.

Lostinspace, it is random, but it doesn't matter.

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Posted · Report post

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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Posted · Report post

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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