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Noobs Weekly: Release II

Week 2: Infinite Quarter Sequence

You are wearing a blindfold and thick gloves. An infinite number of quarters are laid out on a table of infinite area. 20 of these quarters are tails and the rest are heads. How can you can split the quarters into 2 piles where the number of tails quarters is the same in each? You are allowed to move the quarters and to flip them, but you can never tell what state a quarter is currently in.



Note by John Muradeli
2 years, 3 months ago

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Take 20 of the quarters, flip them over and put them in one pile. The other coins go into one infinite pile. If there were \( x \) tails among the finite pile when picked, there will be \( 20 - x \) tails in the infinite pile. As all 20 quarters that were picked have been flipped over, the finite pile will also have \( 20 - x \) tails. \( \blacksquare \) Tan Li Xuan · 2 years, 3 months ago

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@Michael Mendrin Where's your comment gone? I recall you posted a comment here too. Tan Li Xuan · 2 years, 3 months ago

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