frodoskywalker
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Three logicians walk out of the bar
43 votes

At a minimum, one logician - the final one - must be drunk. The first two can reasonably say they don't know if they cannot drive but they think one of the later logicians might The last one ...

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Knights, Knaves and Normals
Accepted answer
31 votes

For the warmup: Should do it. For the challenge: This statement can only work iff the speaker is a knight, as otherwise it will lead to a logical paradox, which is neither true nor false.

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Cards in the darkness
28 votes

Assuming Gerhard's edit reflects what the OP meant to ask, then yes.

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How do I write a "solid" Riddle?
Accepted answer
28 votes

As you say in the question: there should be exactly one interpretation which fits each clue given. However hard the riddle a supermajority of fluent English (or whatever your target language may be) ...

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6 Tries to Guess a Number Between 1-100
24 votes

Yes. Each guess eliminates one number as well as dividing the remaining numbers into 2. One guess can pick a number from 3 (is your number 2?). 2 guesses can do 7. N guesses can pick a number from $2^...

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Is my sibling a sister
Accepted answer
20 votes

The accepted answer has a subtle error. If we randomly select a 2-sibling family with at least one male, the odds of the other being female are indeed 2/3. If we randomly select a male who is part of ...

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The Erasmus dissection of a square
Accepted answer
17 votes

It is not possible. Let v be the set of separations between adjacent vertical lines. Let h be the set of separations between adjacent horizontal lines. Every time an element of v matches an element ...

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Mostly By Way of Emphasis
Accepted answer
15 votes

I believe it is:

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Five Linux command line rebus puzzles
14 votes

Rebus #2 Because Rebus #3 Because

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Connect 3 houses with 3 wells
14 votes

This is impossible Assume 2 houses are fully connected to 3 wells. There must be an 'inner' well which is surrounded by the connections to the other 2 wells. For the third house to be connected to ...

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Number of magic squares with magic constant 0?
13 votes

Take the example square below: -3 2 1 4 0 -4 -1 -2 3 To generate a new square, simply multiply each element of this square by any positive integer. As there are an infinite number of positive ...

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A new stunt at the flea circus
Accepted answer
13 votes

Yes. Start with 0,2,1,3,6,4,8,10,5,7,9,11,22,20,18,16,14,12,24,26,13,15,17,19,21,23,25,27... The pattern is Start with 0,2,1,3 Double Decrement until you cannot Double Increment Divide Increment ...

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A coin flip's long tail
Accepted answer
13 votes

$p$ is a random variable, chosen with uniform probability over the interval [0,1]. The probability of two heads is $\int_0^1 p^2=\frac{1}{3}$, and by symmetry so is the probability of two tails.

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Aquaman's Revenge!
Accepted answer
12 votes

Set the compass to some size, less than the distance from the 5ft mark to the ceiling. Use the bob to find two points on the circle, one directly above the other. Then use the awl to punch holes at ...

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What's the optimal score in the MU-game?
Accepted answer
12 votes

I don't know if this is optimal play for Mary (though I suspect it is), but she can guarantee winning 2 Euros if she initially plays at (5,5) and copies Ursula's moves by translation through (5,5). ...

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Find the width of the river
12 votes

Walk along the river until the rod, held up by my friend at a distance equal to the length of the rope, has the same apparent size as the bridge. Then measure the distance to the bridge in rope ...

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Sleeping students
Accepted answer
11 votes

Professor Kafka is Because

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The lights in the hotel
11 votes

There might be a problem. It looks like Quark's answer of is correct, given this plot for up to 1000 rooms (excess of lights on over lights off) But if we extend that range a little...

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That's a good rebus; I don't know if it's worth $5,000 but it's pretty gosh-patootin' good
Accepted answer
10 votes

Explanation: Clue:

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Different Ball Puzzle
Accepted answer
10 votes

You appear to need 3 weighings. Split your 1023 balls into 3 equal groups of 341. Compare 2 of these, and you know which group the heavier ball is in. Call the heavier group H and one of the normal ...

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Digging a tunnel between random locations
10 votes

Edit: as noted by others, this answer is incorrect. It assumes (incorrectly) that the distance to the modal latitude is the modal distance. $\frac{d}{\sqrt{2}}$ Assume, wlog, that Romeo is at the ...

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Counting numbers with 3 dice
Accepted answer
10 votes

First, each die must have a 0 face. We can see this by noting that we need two 0s to make 001, and a third die with {1,2,3,4,5,6} only gets us to 006. Having this fact, we need 1-8 at least once on ...

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What can't I buy?
Accepted answer
10 votes

We can make $17 \times 8 = 136$ and any number above this by replacing a $17$ with $2 \times 9$, to increment the number by $1$. By the time we run out of $17$s to replace ($9 \times 16$), we continue ...

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Determine what the last number in this series is
Accepted answer
10 votes

The answer is because

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Silly Sven Paints a Highway
Accepted answer
9 votes

Sven will Proof:

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hunting for treasure on an infinite grid
Accepted answer
9 votes

It is Proof: Forget where the pointer is telling you the treasure is, look at where it can't be. For every pointing, there is a 120 degree region (centred opposite the pointing) that the treasure ...

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Fifty-two genuine and two fake coins
8 votes

Step 1: Make 3 groups of 18 coins: A,B,C. Compare A to B and B to C. If A≠B and B≠C then A=C. Select the 'odd' group (assume C) and note if it is lighter or heavier than the others. (assume ...

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A mathematician's coffee alphametic
8 votes

Noting that 3*E gives a different result in the first two columns, there must be an overflow i.e. E is greater than 3. This overflow can only be 1 or 2 (you cannot get more than 27 from tripling a ...

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Knights and Knaves : Liar , Liar - How many are you?
8 votes

The answer is reasoning:

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$100 + n$ boxes for the king!
Accepted answer
7 votes

The limit for n is Because

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