Beach Day by Rodger Bliss
May 2024

Heads or Tails

You are blindfolded and wearing thick gloves. Someone puts twenty coins on the table. Ten of them are heads and ten of them are tails, but you wouldn’t know which because of your blindfold and gloves. You could flip or move the coins if you want. Your goal is to group them into two groups with ten coins each. The two groups should have the same number of heads and the same number of tails. How do you do it?


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5 guesses to Heads or Tails

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  • Sid

    Flip five each from both the groups in the opposite way of the original ones.

  • Dude

    Since you don’t know which are which (because you’re blindfolded) that method will not work.

    Keep trying.

  • Elvis

    first separate them into the two groups of ten, now one group has, lets say, three head facing coins and seven tail facing coins. therefore the other set has seven head facing coins and three tail facing coins. Now all you do is flip all the coins of one group and both sets with have an even number of tails and heads

  • Simple. Take of your gloves and blindfold

  • Dude

    Elvis, you are correct.

    Create a subgroup of any 128 pennies. Then flip over all 128. That group of 128 and the group of all the remaining pennies will have the same number of heads facing up.
    This works because the “tails” that you grab while making your subset of 128 will equal the “heads” that are left in the original pile. Once you flip your 128 coins over, these “tails” will turn into “heads” and the two groups will have a matching number of heads-up coins.

    You are today’s winner.