Archive for the ‘Riddles’ Category
Monday, August 13th, 2007
(you can find the original riddle here)
Let's begin with a draft solution, one that doesn't work but will start us in the right direction. And to keep things simple, let's say all the tasks are done the minute the prisoners leave the meeting, so all they have left is to ...
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Wednesday, August 1st, 2007
In an effort to make this blog more interactive, I'm switching the riddles to a new format. I'll first post only the riddle, without the solution, so you guys can have a crack it. After a week or so, I'll post the solution. Here goes...
[tex]n[/tex] prisoners are planning an escape. ...
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Monday, August 7th, 2006
McDonald's sells its Chicken McNuggets in groups of 6, 9, and 20. What is the largest number of McNuggets you can't buy?
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Saturday, July 8th, 2006
Four coins are placed on a round table, in positions north, east, south, and west. The room is dark, so you can't see the coins. Your goal is to get all coins to be on the same side -- heads or tails. In each turn you can choose to flip ...
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Thursday, June 29th, 2006
Here's a nice one. Show that, for any prime number p other than 2 and 5, there is a multiple of p that is written as a series of 1's in decimal representation. For example, 111 is a multiple of 3, and 11 is a multiple of itself. Hint: Use ...
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Monday, June 12th, 2006
You have a 1 meter long stick and 100 ants. The ants are somehow distributed on the stick, and each ant moves either right or left at 1 meter/second. When two ants meet, they both instantaneously turn around and start walking in opposite directions, still at 1 meter/second. When an ...
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Sunday, June 4th, 2006
As promised, here's another solution to the two envelopes riddle: First, choose a descending list of probabilities p(n). When you receive a number n, say 'higher' with probability p(n) and 'lower' otherwise. That's the solution. Now let's prove that it works.
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Saturday, May 27th, 2006
Players A and B play a game. Player A somehow selects two different natural numbers and puts them in two envelopes. He then chooses one envelope at random and hands it to player B. Player B looks at the number, and has to guess whether the number in the other ...
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