Hard riddles and difficult puzzles

Very hard brain teasers. For real geeks only!


Parents buy cookies for their kids. They are saving money so they buy two discounted ones (few days after best before). They don’t want to look greedy so they also buy two cookies for the full price.

When they come home their two kids grab cookies, and each get two. They don’t check best before so their choice is random.

Do you think that life is fair and each kid gets one expired and one good cookie? Or one kid gets both expired? What is more likely to happen?

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Prison guards are bored so during dinner they announce the prisoners that they will play a game:

In the morning they will stand in a line so that every prisoner will see all standing in front of him but no one behind him. Guards will randomly paint red or white stripe on their back.

They will ask prisoners one by one from the last to the first. They will be allowed to say just one word “red” or “white”. If the prisoner says the color he has on his back he may go home in opposite case he will be executed without delay.

The prisoners are in one cell during the night and they can discuss the tactics.

Which is the best? How many will survive?

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Thirteen coins

There are 13 exactly same looking coins. One of them has slightly different weight than the others – we don’t know if it is heavier or lighter. Can you tell in 3 scalings which one it is using even arm balance?

If this riddle by any chance seemed too easy for you, try 40 coins in 4 scalings – the principal is the same.

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