From - Tue Sep 2 09:38:11 1997
From: [email protected] (Matthew Daly)
Newsgroups: rec.puzzles,rec.answers,news.answers
Subject: [FAQ] rec.puzzles Frequently Asked Questions [weekly]
Followup-To: poster
Date: 1 Sep 1997 20:03:50 GMT
Organization: Eastman Kodak Company
Lines: 478
Summary: This posting contains a list of puzzles that appear more often
than one would hope on rec.puzzles, and information about the
rec.puzzles archive, which contains many common and interesting
puzzles. Please examine both before posting to rec.puzzles.
Originator: daly@crestone
Archive-name: puzzles/faq
Posting-frequency: weekly
Rec-puzzles-archive-name: puzzles/faq
Last-modified: Mon August 25 1997
Version: 1.335
Welcome to the rec.puzzles Frequently Asked Questions List. The purpose of
this article is to assist readers in determining if their nifty new puzzle
is not quite so nifty or new after all and to introduce new readers of
rec.puzzles to newsgroup etiquette. Questions and comments about this FAQ
should be emailed to [email protected]
This FAQ is maintained by Matthew Daly, [email protected] and posted weekly
or thereabouts.
0. INTRODUCTION AND CONTENTS
The rec.puzzles newsgroup is generally friendly, and the signal-to-noise
ratio is quite high compared with many other Usenet newsgroups. However,
many rec.puzzles readers have a MAJOR PET PEEVE -- seeing the same old puzzles
(and the same old answers, and the same old discussions) over and over again.
One of the entertaining pastimes of rec.puzzles is "sport-flaming", where the
regulars attempt to enliven a puzzle by taking advantage of poor wording or
by simply making it clear that the puzzle poster should have read the FAQ or
checked the archives before posting. If you have been sport-flamed, please
don't take it personally, and PLEASE don't start a real flame war over it.
Nobody is trying to force you from the newsgroup: it's merely a good-natured
way of pointing out that you should have been more cautious before posting.
When you've been around for a couple months, you'll understand why, and if
you've seen netcops in other Usenet groups, you will probably appreciate our
more entertaining style.
0. Introduction and contents.
1. What you should do before you post a puzzle.
2. Frequently asked puzzles (specific).
2.1. You have 12 coins, one of which is either light or heavy...
2.2. What are the three common English words that end in -GRY?
2.3. The bellboy (where is the missing dollar?).
2.4. What's the probability that my other child is a girl?
2.5 Monty Hall (should I switch doors?)
2.6 How quickly can the four men cross the bridge?
3. Frequently asked puzzles (general).
3.1. Lateral Thinking (or Situation) puzzles.
3.2. Sequence puzzles.
3.3. English language records.
3.4. Logic puzzles.
3.5. The Equation Analysis Test (26 = L. of the A.)
4. Posting puzzle solutions.
5. Information about the rec.puzzles archive.
5.1. The archive index.
5.2. Accessing individual puzzles.
5.3. Getting to the archive by FTP, gopher, and WWW.
6. Information about the rec.puzzles oracle.
7. Credit where credit is due.
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1. WHAT YOU SHOULD DO BEFORE YOU POST A PUZZLE:
If the puzzle that you want to post came from a photocopy of a puzzle, or an
email from a friend, it is extremely likely that the puzzle has been in
rec.puzzles before. Before you post any puzzle to rec.puzzles, you should
take the following steps to ensure that the puzzle is not an oldie:
o Read the newsgroup for at least a week (Reading for some time before
posting is proper etiquette for ANY Usenet newsgroup. If you did not
realize that, it would be a good idea to read news.announce.newusers.)
o Read this article. (Good for you! You're doing it!)
o If you have access to a Usenet archiver like http://www.dejanews.com
check some obvious keywords to see if your puzzle has been discussed
in the past several months.
o Look through the rec.puzzles archive (see Section 5 below). If you
can't tell whether your puzzle is in the archive (it's not always
clear from the index), ask the oracle.
o Ask the rec.puzzles oracle (see Section 6 below).
If what you really want is not to pose your question for the puzzlement of
rec.puzzles readers, but rather simply to find out the answer to the puzzle
(presumably fairly quickly), you'll generally get a faster turnaround from
searching the archives and/or the oracle than posting to the newsgroup.
----------------------------------------------------------------------
2. FREQUENTLY ASKED PUZZLES (SPECIFIC):
This section contains, in no particular order, short summaries of the most
commonly occurring puzzles on rec.puzzles. Unless you have some really
devastatingly new twist or observation on these puzzles, don't post about it.
In this section, and throughout the FAQ, the phrases between arrows
==> like this <== are the names of puzzles as they appear in the
archive. The stuff in [square brackets] is the name of the file you
should look for, once you're in the rec.puzzles archive directory, if
you are accessing the archive by ftp (see Section 5.3 below).
2.1. ==> balance <== [logic/part5]
You have 12 coins, one of which is counterfeit. The counterfeit is
indistinguishable from the rest except that it is either heavier or
lighter (but you don't know which). How can you determine which coin
is the counterfeit and if it is heavy or light in 3 weighings on a
balance scale?
This puzzle, which is quite a challenge to solve, is annoying for
two reasons. First, it gets posted quite a bit. Second, it always
seems like the first person to respond to the post is wrong.
The archive gives a very good solution to the generalized version of
the problem, but an especially elegant solution to the 12-coin version
is to label the coins A,C,D,E,F,I,K,L,M,N,O,T and weigh the coins as
follows: MA DO -- LIKE, ME TO -- FIND, FAKE -- COIN. Simple logic
will now suffice to find the odd coin. For instance, if the results
of the weighings are left down, balance, and left down, then the
only consistent result is that coin "A" is heavy.
2.2. ==> gry <== [language/part2]
What are the three common English words that end in -GRY?
There are only two: "angry" and "hungry". The rec.puzzles archive lists
a large collection of words that end in -GRY, but none of them could be
considered even remotely common.
There are a plethora of "trick" answers to the problem, most of which
depend on a sly wording of the question or that the question be spoken
instead of written. Several "experts" have claimed to have tracked this
question back to an original form and provided a solution based on that
specific wording -- the fact that these original forms vary among experts
is dismaying, though. It is the belief of the FAQ maintainer that the
general question is not intended to have an general answer, and that any
efforts to label any answers as "correct" only prolongs a tired debate.
In 1996, the word "nugry" was coined to provide an answer to this puzzle
(and we are working hard to make it a commonly-used word). It was first
used by Tom Maciukenas ([email protected]) and its definition is:
nugry (noo-gree or nyu-gree) n. 1. A newcomer who fails to follow
established rules or procedures. 2. One who shows his inexperience by
acting inappropriately. 3. One who posts the -GRY puzzle to rec.puzzles,
in violation of the FAQ. --adj., Having the qualities of a nugry.
--nugrily, adv., pl. nusgry (news-gree), nugries
2.3. ==> 29 <== [logic/part1]
Three men in a hotel share the $30 cost of a common room. The hotel
manager realized that they should have paid only $25 for the room,
so he sends the bellboy up with five $1 to give to the men. But
the unethical bellboy only gives $1 to each of the men and pockets
the remaining $2. Now, each of the men has paid $9 for his room
and the bellboy has $2, so where is the missing dollar?
There is no "missing dollar". The $27 paid by the men includes
the $2 pocketed by the bellboy, so it makes no sense to add these
numbers.
2.4. ==> oldest.girl <== [probability]
If a person has two children, and answers "yes" to the question "Is at
least one of your children a girl?", what is the probability that both
children are girls?
The answer is 1/3, assuming that it is equally likely that a child
will be a boy or a girl. Assume that the two children are named Pat
and Chris -- the three equally-likely cases are that Pat is a girl and
Chris is a boy, Chris is a girl and Pat is a boy, or both are girls.
Since one of those three equally likely possibilities have two girls,
the probability is 1/3.
2.5. ==> monty.hall <== [decision]
Three doors; one has a prize. If you pick the door with the prize, you
get the prize. You pick a door, Monty Hall opens a different door that
does not contain the prize and allows you the right to switch you
choice to the remaining unopened door. Should you switch?
The answer is that it is advantageous to switch: your probability of
winning the prize is 2/3 if you do so. The probability that your
first guess is wrong is obviously 2/3, and switching doors will gain
you the prize if and only if your first guess was wrong.
The solution assumes that Monty knows which door contains the prize
and that his decision to offer you the switch is independent of
whether you originally chose the correct door. These assumptions are
implicitly made because they were the way the game was conducted by
Monty Hall on "Let's Make A Deal" -- if you don't consider these
assumptions to be natural then your conclusions may be different.
2.6. Four men are on one side of a rickety bridge on a dark night. The
bridge is only strong enough to support two men at a time. It is
also necessary for the men crossing the bridge to carry a lantern to
guide their way, and the four men have only one lantern between them.
Andy can cross the bridge in 1 minute, Ben in 2, Charlie in 5, and
Dan in ten minutes. How quickly can all four men be together at the
other side?
The solution is surprising to some people because they initially
suspect that it is fastest if Andy escorts everyone across because
he can return the fastest. However, a faster method requires only
17 minutes. First, Andy and Ben cross (2 min), then Andy returns
(1 min). Then, Charlie and Dan cross (10 min) and Ben returns (2 min).
Finally, Andy and Ben recross (2 min). In short, you save two minutes
by having the two slowest people cross the bridge in the same trip.
----------------------------------------------------------------------
3. FREQUENTLY ASKED PUZZLES (GENERAL):
This section gives information on some general categories of puzzles
that pop up over and over again.
3.1. ==> situation.puzzles <== [logic/part3 and logic/part4]
A man walks into a bar, asks for a drink, the bartender points a
gun at him, the man says "thank you" and leaves.
The essence of these puzzles is that one person in a group answers a
series of yes/no questions and the other people in the group attempt
to piece together the circumstance that would lead to the posed
situation. Over the years, rec.puzzles has referred to these as
"situation puzzles", although a suite of books by Paul Sloane has made
the term "lateral thinking puzzles" more commonplace.
Because very few of the lateral thinking puzzles posted to rec.puzzles
are original and the structure of Usenet is not conducive to posting
and answering yes/no questions, moderating contests of this sort in
rec.puzzles is a bad idea. Fortunately, Sloane manages a very popular
website where several original puzzles are moderated at a time. To join,
go to http://www.books.com/forum/101 and subscribe.
The answer to the puzzle given above is that the man had the hiccups,
intended to cure them by drinking a glass of water with his nose plugged,
and was glad that the bartender scared him enough to cure him.
3.2. Sequence puzzles
O, T, T, F, F, S, ? ==> series.06 <== [series]
5, 6, 5, 6, 5, 5, 7, 6, ? ==> series.21 <== [series]
...
The problem with letter sequences is that we've seen most of them,
quite possibly even that one you just thought of all by yourself.
Check out the archive, in the general category "series", to make sure
yours isn't there.
The problem with number sequences is that many puzzlers find them
unsatisfying, since there are infinitely many formulas that will fit
any finite sequence, and the concept of "simplest" or "best" formula
is a slippery one. Since number sequences inevitably lead to the same
old discussion, it's probably best to avoid them in rec.puzzles.
In spring 1994 Sloane announced a nifty new service, the On-Line
Encyclopedia of Integer Sequences. To look up a sequence, send
e-mail to [email protected] containing up to five requests
like the following:
lookup 4 9 16 25 36
The reply will report all sequences in the encyclopedia (up to a limit
of seven) that match your sequence. An empty message to that address
will get you more detailed instructions. For further information,
send email to [email protected].
3.3. English language records
What's the shortest sentence with all 26 letters? ==> pangram <==
What's the longest one-syllable word? ==> syllable <==
(all of those are in: [language/part2])
These and zillions of other questions -- almost anything you could
ever think of -- are answered under the general archive category
"language".
3.4. Logic puzzles
Some overly familiar logic puzzles from the archive are:
==> number <== [logic/part1]
Mr. S and Mr. P are "perfect logicians". Mr. S is given the sum
of two numbers; Mr. P is given their product. The following
conversation ensues. ...
==> unexpected <== [logic/part5]
Swedish civil defense authorities announced that a civil defense
drill would be held one day the following week, but the actual
day would be a surprise. ...
==> fork.two.men <== [logic/part4]
Two men stand at a fork in the road. One fork leads to Heaven;
the other fork leads to Hell. One of the men always answers
the truth to any yes/no questions asked of him, the other always
lies. Can you find one question that will allow you to determine
the road to Heaven?
Before you post a logic puzzle to rec.puzzles, see the archive
category "logic", especially the subcategory "logic/smullyan". Better
still, read all of Smullyan's books.
3.5 The Equation Analysis Test
==> equations <== [language/part1]
26 = L of the A (Letters of the Alphabet)
8 = S on a SS (Sides on a Stop Sign)
The original form of the Equations Analysis Test was created by'
Will Shortz for Games Magazine, although the test is still widely
distributed without the proper credit. Posting the original quiz
(which includes the two above examples) is quite unnecessary, as
the archive includes all of the originals plus several hundred
extra equations. If you come up with your own set, it is on-topic
to post them, although you want to be sure to follow-up with your
solutions within a week because many of them are hard to guess with
certainty.
----------------------------------------------------------------------
4. Posting puzzle solutions
When someone posts a puzzle that you know the solution to, or better yet,
a puzzle that you discover the solution to after hours of thinking, it's
natural to want to post the solution to proclaim your achievement to the
world. Such posts are called "spoilers". There's nothing wrong with
posting a spoiler, but certain guidelines should be followed.
When you post a spoiler, you should include the warning [SPOILER] after
you quote the puzzle, but before you include your solution. (Some people
also include [SPOILER] in the subject line of their post.) After the
[SPOILER] flag, insert a page break by pressing Ctrl-L; it should look
like this: ^L. The page break will cause many newsreaders to pause at
that point and give the reader a chance to move on to the next post if
they'd rather wait before reading your spoiler. If your editor doesn't
allow pagebreaks, 24 or more blank lines will do.
For people who *do* want to read your spoiler, it's a good idea to show
your work. When someone chooses to read a spoiler, it's usually because
that person has given up on solving the puzzle on his own, and wants to
know how to solve it. A bare answer isn't as informative or entertaining.
----------------------------------------------------------------------
5. THE rec.puzzles ARCHIVE
The rec.puzzles archive is a treasure trove of puzzles and their
solutions. Maintained by Chris Cole, the archive currently contains
over 500 puzzles, including those mentioned in this FAQ, and others
of many varieties. (It is not, as the name might suggest, an archive
of all posts made to rec.puzzles.)
Corrections to and comments on archive entries should be emailed to
[email protected]. Discussion of the solutions in the
archive is generally welcomed in rec.puzzles.
5.1. The archive index
The easiest way to figure out the archive is to get and read the
index. The index contains brief descriptions of all of the puzzles in
the archive. To request a copy of the index, send email to
[email protected], with a body that looks like this:
return_address your_name@your_site.your_domain
send index
For example, if your net address is "[email protected]", send this
message:
return_address [email protected]
send index
5.2. Accessing individual puzzles
Individual puzzles from the archive may be requested by sending email
to the same address as above, containing one or more lines of the form
send