MonkeypuzzlesPuzzles not even a monkey could solve. A collection of
the greatest puzzles in the world.http://monkeypuzzles.org/2012-09-02T00:00:00+00:00Adam RenbergOlle WermeOne lies, one always tells the truth2012-09-02T00:00:00+00:00
<p>As you walk along a path in a forest, the path splits in two. You do not know
which way to go. At the junction, two solemn guards stand, ready to help any
passersby.</p>
<p>It so happens that the guards only know the words <em>yes</em> and <em>no</em>. It also
happens to be that the guards are twin brothers, impossible to tell apart.
And, as twin brothers, the guards have developed a quite peculiar dynamic:
One of them always tells the truth, while the other always lies.</p>
<p>You have one question, which you can ask only one of the guards. How do you
determine how to continue on your path?</p>
UnknownBlue eyes2012-08-05T00:00:00+00:00
<p>On an island in the middle of the ocean lives several people of a peculiar
sort: They are all logicians. One hundred of them have blue eyes, while the
others have brown eyes. The leader of the group, known as the guru, has green
eyes. It so happens that no one on this island knows the color of their own
eyes.</p>
<p>At midnight every night a ferry arrives at the island, and leaves shortly
thereafter with anyone who can tell the ferryman their eye color.</p>
<p>One day, the guru stands up and says, so that everyone hears:</p>
<p>"I can see at least one person with blue eyes."</p>
<p>What will happen? Will anyone leave the island? Who, and when?</p>
<p>Please not that no one will tell anyone else their eye color, or communicate
it in some other. As soon as someone knows their eye color she will leave the
island with the next ferry - they all want to leave this weird place, after
all. During any given day, all islanders will see each other, and notice any
absences.</p>
UnknownCrossing a bridge in the dark2012-08-05T00:00:00+00:00
<p>Four people are walking in the dark, and they have only one torch. They
stumble upon a long and narrow bridge, which they need to cross. To cross the
bridge they need the torch, and once it has been carried to the far side,
someone needs to bring it back to the ones who are waiting. Only two can
cross the bridge at the same time.</p>
<p>One of the group is quite slow and takes 10 minutes to cross the bridge. The
others take 5, 2 and 1 minutes, respectively.</p>
<p>What is the fastest way for the group to cross the bridge?</p>
UnknownGame show: Three doors, one treasure2012-08-05T00:00:00+00:00
<p>You participate in a game show, and in the final contest the host presents
you with three doors. Behind one door is one million dollars. The other two
hide sacks of potatoes.</p>
<p>The host asks you to choose one door. After you have
done so, the host will open one door - always one of the doors you didn't
choose, and always one hiding a sack of potatoes.</p>
<p>Now there are only two doors left - the one you've chosen, and one more. The
host asks you:</p>
<p>"Do you want to switch doors?"</p>
<p>What should you do to maximise your chances of getting the million dollars?</p>
UnknownGuess 1, 2 or 32012-08-05T00:00:00+00:00
<p>Martin thinks of a number, 1, 2 or 3. Sophie is allowed to ask Martin one
yes-or-no question, to which he will answer "yes", "no", or, if he doesn't
know the answer, "I don't know".</p>
<p>What question should Sophie ask Martin to uncover his number?</p>
UnknownInfinite hotel, variant 12012-08-05T00:00:00+00:00
<p>The well-renowned hotel of Bilzebab is famous for having an infinite number
of rooms, and, being such a famous and well-renowned hotel, the hotel is
fully booked.</p>
<p><em>Ten tourists</em> arrive at the hotel and ask if there are any rooms available
for them.</p>
<p>Bilzebab is also famous for having a smart and quick-thinking manager. The
manager thinks for a minute, and then says:</p>
<p>"Yes, of course, I'll just reorganize the current arrangements, and you will
all get a room".</p>
<p>In which rooms will the newcomers stay?</p>
<p>Please note: After the manager has reorganized the room arrangements, no one
will share a room, no one will be thrown out, and the hotel will still be
fully occupied.</p>
<p>Each person, including the one already with rooms, will have to be given a
specific, calculable, new room number. Saying "go to room infinity plus 1" is
not valid.</p>
UnknownInfinite hotel, variant 22012-08-05T00:00:00+00:00
<p>The well-renowned hotel of Bilzebab is famous for having an infinite number
of rooms, and, being such a famous and well-renowned hotel, the hotel is
fully booked.</p>
<p>An <em>infinite number of tourists</em> arrive at the hotel and ask if there are any
rooms available for them.</p>
<p>Bilzebab is also famous for having a smart and quick-thinking manager. The
manager thinks for a minute, and then says:</p>
<p>"Yes, of course, I'll just reorganize the current arrangements, and you will
all get a room".</p>
<p>In which rooms will the newcomers stay?</p>
<p>Please note: After the manager has reorganized the room arrangements, no one
will share a room, no one will be thrown out, and the hotel will still be
fully occupied.</p>
<p>Each person, including the one already with rooms, will have to be given a
specific, calculable, new room number. Saying "go to room infinity plus 1" is
not valid.</p>
UnknownInfinite hotel, variant 32012-08-05T00:00:00+00:00
<p>The well-renowned hotel of Bilzebab is famous for having an infinite number
of rooms, and, being such a famous and well-renowned hotel, the hotel is
fully booked.</p>
<p>An <em>infinite number of buses</em>, each with an <em>infinite number of tourists</em>,
arrive at the hotel and ask if there are any rooms available for them.</p>
<p>Bilzebab is also famous for having a smart and quick-thinking manager. The
manager thinks for a minute, and then says:</p>
<p>"Yes, of course, I'll just reorganize the current arrangements, and you will
all get a room".</p>
<p>In which rooms will the newcomers stay?</p>
<p>Please note: After the manager has reorganized the room arrangements, no one
will share a room, no one will be thrown out, and the hotel will still be
fully occupied.</p>
<p>Each person, including the one already with rooms, will have to be given a
specific, calculable, new room number. Saying "go to room infinity plus 1" is
not valid.</p>
UnknownPirates sharing treasure2012-08-05T00:00:00+00:00
<p>Five pirates have found a treasure chest containing one hundred coins, and
are now in the process of dividing the treasure among themselves. In their
usual democratic fashion they decide that the oldest of them will decide on
how split up the treasure. After he has made his decision they will all vote
to accept or reject his plan.</p>
<p>If at least half of them vote to reject the plan, the oldest pirate gets
thrown overboard, and the process is restarted with the next-to-oldest coming
up with the plan, and so on.</p>
<p>Given that the pirates are all trying maximise the amount of treasure they
get, how should the oldest pirate propose they share it?</p>
<p>Keep in mind that they, as proper pirates, are all perfectly logical and
rational. And getting no coins is just as bad as getting thrown overboard.</p>
UnknownShaking hands at a party2012-08-05T00:00:00+00:00
<p>Rebecca and her partner attend an evening party together with four other
couples. During the initial mingling, everyone greets and shakes hands with
those they hadn't met before.</p>
<p>Later in the evening Rebecca asks all nine other party-goers how many people
they shook hands with, and she gets nine different answers.</p>
<p>How many people did Rebecca shake hands with?</p>
<p>Please note that everyone had met their partner prior to the party, and that
no one shook hands with themselves.</p>
UnknownTen piles of coins2012-08-05T00:00:00+00:00
<p>There are ten piles of coins, and ten coins in each pile. Each coin in each
pile weighs 1 gram, except for one pile where the coins weigh 1.1 grams.</p>
<p>You have a digital scale, and you are allowed one attempt at using it. You
can take any number of coins from any number of piles. How do you determine
which pile has the heavier coins?</p>
UnknownThe devil's gate2012-08-05T00:00:00+00:00
<p>As people die they sometimes go to hell. The devil, the nice bloke that he
is, gives them a chance to escape and go to heaven.</p>
<p>He lines them up outside the gates of hell and gives them each a hat, black
and white hats distributed randomly. No one gets to see the color of their
own hat, but they can see the hats of everyone in front of them.</p>
<p>The devil approaches the person standing last in the line an asks for the
color of his hat. If the answer is correct he escapes; if not, his stay in
hell is final. The devil then proceeds to the next-to-last person in the
line, and so on.</p>
<p>One hundred people have now died and they decide to come up with a strategy
to help as many of them as possible to escape into heaven. They know that
when they stand in line the only words the will be able to say are 'black'
and 'white'.</p>
<p>What strategy should they use? How many can be saved?</p>
<p>Please note: When they stand in line, everyone can see only the people in
front of them, but everyone can hear the people behind them's answer to the
devil. Also note that the guy last in line can never be save for sure. No one
but the devil knows his color.</p>
UnknownThe farmer with a goat, a cabbage and a wolf2012-08-05T00:00:00+00:00
<p>A farmer with a goat, cabbage and a wolf is standing on the side of a river.
They need to cross it, but there is only a small row boat that only can fit
two of them.</p>
<p>The goat is hungry, so if the farmer leaves the goat alone with the cabbage,
the goat will eat the cabbage. The wolf is also hungry, and it will eat the
goat if they are left alone.</p>
<p>How should the farmer proceed to get them all across the river?</p>
UnknownThe mirrored clock2012-08-05T00:00:00+00:00
<p>A girl leaves her home in the morning for school. She looks for the time on
an old-fashioned, analog clock, through a mirror. Unfortunately there are no
digits on the clock, so she mistakes the mirror image for the actual time.
She rides her bike to school, which takes twenty minutes. When she arrives
and looks at the school clock, it shows a time two-and-a-half hours later
than the mirror image she saw at home.</p>
<p>What was the time when she left home? What was the mirror image? And when did
she arrive?</p>
<p>Note: There can be different answers, depending on whether she sees the
length difference of the two clock arms (hour and minute) or not. There is at
least one answer if she can see the length difference, and another answer if
she can't.</p>
UnknownThree boxes with incorrect labels2012-08-05T00:00:00+00:00
<p>You have three boxes in front of you, one with <em>nails</em> in it, one with
<em>screws</em>, and one with both <em>nails and screws</em>. The boxes all have
labels describing their contents. Unfortunately, all labels are incorrect,
and describes one of the other boxes.</p>
<p>You can pick up one item from one of the boxes (no peeking). How do you
determine what is in each box? Put another way: From which box, with which
label, do you take an item?</p>
UnknownThree hats2012-08-05T00:00:00+00:00
<p>The great town wizard needs a new apprentice, and has announced a competition
for the post. Many applicants have tried, and only the three brightest remain
for the final challenge.</p>
<p>The wizard gives each applicant a hat, and tells them that they have either a
black or a white hat. The first one to figure out the color of her own hat
and publicly announce it wins the challenge, and becomes the wizard's
apprentice. Also, if any of them sees another applicant having a white hat,
they are supposed to say:</p>
<p>"I see someone with a white hat."</p>
<p>However, the wizard, devious as she is, has given white hats to all three
applicants. So, predictably, they all immediately announce that they see
someone with a white hat, and then nothing happens for a while.</p>
<p>But, after a few minutes of silence, the most clever of the applicants
announces: I have a white hat! She becomes the wizard's apprentice, and
everyone lives happily ever after.</p>
<p>How can she know the color of her hat?</p>
UnknownThree pearls in three lockers2012-08-05T00:00:00+00:00
<p>There are three lockers, each with two drawers. Each drawer contains one item
- a pearl, or a clump of coal. In one locker both drawers contain pearls, in
another both lockers contain clumps of coal. In the third locker one drawer
contains a pearl, and the other contains a clump of coal.</p>
<p>You do not know which locker is which. You open one drawer and find a pearl.
If you are allowed to open one more drawer, which one should you open to
maximise your chances of finding another pearl?</p>
UnknownWeighing eight stone balls2012-08-05T00:00:00+00:00
<p>You have eight small stone balls, where one is slightly heavier than the
others. You have an old-fashioned balancing scale. In as few weighings as
possible, how do you find the heavier ball?</p>
UnknownWeighing twelve stone balls2012-08-05T00:00:00+00:00
<p>You have twelve small stone balls, where one is of slightly different weight
than the others, either lighter or heavier - you don't know. You have an
old-fashioned balancing scale. In as few weighings as possible, how do you
find the odd ball?</p>
UnknownThree switches2012-07-01T00:00:00+00:00
<p>An old-fashioned light bulb hangs from the ceiling of an otherwise empty
room. A door leads outside, where three swithces sit on the wall. One of the
switches control the light bulb - how do you figure out which switch it is?</p>
<p>You cannot see from outside the room if the light bulb is on or off, and you
are only allowed to enter the room once. The light bulb and all the switches
are initially in their off position. You are allowed to flip the switches any
number of times, and you can take as long as you want before answering.</p>
<p>Use your common sense ;)</p>
Unknown