Answer One: A Secret Box
Original Problem
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You lock the box with your lock and send it to your friend. Your friend locks it with his lock and send it back to you. You unlock your lock, and send it to your friend, who can then unlock her lock and open the box.
This is actually an analogy of how RSA and web encryption works.
Answer Two: Seagull’s Crisis
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39 Days
If there are 1 seagulls infected, the one infected seagull knows at least one of them is infected but he can’t see any infected seagulls therefore he is the one infected. He kills himself.
If there are 2 seagulls infected, he thinks, if there are only one seagull infected, then he would have killed himself already. So there must be at least one more infected seagull. But I can’t see any other infected seagulls, therefore I must be infected. He kills himself.
Following this train of thought, after the 39th meeting, all 39 seagulls would have realized that if there were only 38 infected seagulls, they all would have commited suicide after the 38th meeting. Therefore I’m infected, and thus kill himself.
Answer Three: The Escape
Original Problem
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You ’saw’ yourself in the mirror, you take the ’saw’ and saw the table in half. Two halves make a ‘hole’. You climb out of the hole.
Answer Four: The Mystery Sequence
Original Problem
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10,000,000,000
The sequence is in order of the number of letters in the number’s English spelling. I.E. ten=3, nine=4, sixty=5, etc…
Answer Five: Who Are We?
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They belong to Set 1.
Set 1 contain all letters without curves, set 2 contain all that have curves.
Answer Six: The Line
Original Problem
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Each man joins the line in the middle where black and white hats meet. They really don’t even have to make assumptions about the color of their own hats.
Answer Seven: Critical Moment
Original Problem
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Door C
Originally, there’s a 1/3 chance for you to select the right door and 2/3 for you to select a wrong door. Once a wrong door is eliminated, by switching, you will always switch to the other choice (i.e. if you chose the right door originally, you’d switch to the wrong door, and vice versa). Thus, if you switch, you’ll have a 2/3 chance of getting the right door and 1/3 change of getting the wrong door.
Answer Eight: Buckets of Water
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Fill up the 5 gallon bucket.
Fill up the 3 gallon bucket with the 5 gallon bucket.
Empty the 3 gallon bucket.
Pour the 2 gallons remaining in the 5 gallon bucket into the 3 gallon bucket.
Fill up the 5 gallon bucket.
Pour one gallon from the 5 gallon bucket into the 3 gallon bucket, thereby filling up the 3 gallon bucket.
Empty the 3 gallon bucket.
You now have 4 gallons in the 5 gallon bucket!
Answer Nine: Einstein’s Puzzle
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This solution requires a lot of tinkering with logic. See the details here.
Answer Ten: The Fifteen Game
Original Problem
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If you write down a magic square with numbers 1 through 9 (i.e. every row, column, diagnal sums to 15) you’ll get something like
4|9|2
——
3|5|7
——
8|1|6
Now the game is just like tic-tac-toe!