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Path: senator-bedfellow.mit.edu!bloom-beacon.mit.edu!news-out.internetmci.com!newsfeed.internetmci.com!206.229.87.25!news-peer.sprintlink.net!news-sea-19.sprintlink.net!news-in-west.sprintlink.net!news.sprintlink.net!Sprint!159.56.2.2!thetimes.pixel.kodak.com!news.kodak.com!newsserver.rdcs.Kodak.COM!crestone!daly From: mwdaly@kodak.com (Matthew Daly) Newsgroups: rec.puzzles,rec.answers,news.answers Subject: [FAQ] rec.puzzles Frequently Asked Questions [weekly] Followup-To: poster Date: 20 Oct 1997 13:58:29 GMT Organization: Eastman Kodak Company Lines: 478 Approved: news-answers-request@MIT.EDU Message-ID: <62fo25$t8s$1@kodak.rdcs.Kodak.COM> Reply-To: mwdaly@kodak.com NNTP-Posting-Host: 129.126.74.4 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 Xref: senator-bedfellow.mit.edu rec.puzzles:88409 rec.answers:34900 news.answers:115045 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 mwdaly@kodak.com This FAQ is maintained by Matthew Daly, mwdaly@kodak.com 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. ---------------------------------------------------------------------- 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 (tomm@dvorak.amd.com) 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 sequences@research.att.com 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 njas@research.att.com. 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 archive-comment@questrel.com. 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 archive-request@questrel.com, with a body that looks like this: return_address your_name@your_site.your_domain send index For example, if your net address is "mickey@disneyland.com", send this message: return_address mickey@disneyland.com 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 <puzzle-name> where <puzzle-name> is the name by which the puzzle is called in the archive index. You may use the full name or just the last part of it. For example, to request the 12-coins problem (see Section 2 above), either of the following "send" lines will work: send logic/weighing/balance send balance You may also request multiple puzzles by putting multiple "send" lines in your request message. Please refrain from requesting the entire archive by email. Use FTP. 5.3. Getting to the archive by FTP, gopher, or WWW FTP The entire archive is also accessible via anonymous FTP, from any site which maintains archives of the newsgroups news.answers or rec.answers. The file part01 contains the index. The remaining files contain alternating problem text and solution text for all the puzzles. Some FTP sites are: North America: ftp://rtfm.mit.edu/pub/usenet/news.answers/puzzles/archive ftp://ftp.uu.net/usenet/news.answers/puzzles/archive ftp://mirrors.aol.com/pub/rtfm/usenet/news.answers/puzzles/archive ftp://ftp.cis.ksu.edu/pub/mirrors/news.answers/puzzles/archive Europe: ftp://ftp.cs.ruu.nl/pub/NEWS.ANSWERS/puzzles/archive ftp://src/doc.ic.ac.uk/usenet/news-faqs/news.answers/puzzles/archive ftp://uni-paderborn.de/doc/FAQ/rec/puzzles Asia: ftp://ftp.hk.super.net/mirror/faqs/puzzles/archive GOPHER From the global home page, the menu choices to access the archives at "cs.ttu.edu" are: North America/USA/Texas/Texas Tech University, Computer Sciences /Entertainment/Games/Puzzles To access "uni-hohenheim.de" your menu choices are: Europe/Germany/University of Hohenheim/Lots of Interesting Stuff /FAQ Frequently Asked Questions/rec/puzzles/archive WAIS wais://xraysgi.ims.uconn.edu:8000/rpa WEB http://einstein.et.tudelft.nl/~arlet/puzzles/index.html Partially HTMLized. http://www.nova.edu/Inter-Links/puzzles.html http://xraysgi.ims.uconn.edu A keyword search plus links to other puzzle sites ---------------------------------------------------------------------- 6. THE rec.puzzles ORACLE This is a group of rec.puzzles regulars, who are familiar with the rec.puzzles archive, and who will find your answer there if it exists, or maybe compose an original answer if they are interested enough! At any rate, they promise to respond to your question within two days, and perhaps save you the embarrassment of posting a well-worn puzzle. They will respond within two days even if they do not know the answer to your question. To query the rec.puzzles oracle, send email containing your question to puzzle-oracle@questrel.com. Comments and suggestions are always welcome at the same address. ---------------------------------------------------------------------- 7. CREDIT WHERE CREDIT IS DUE The original rec.puzzles FAQ was written by Tom Magliery, mag@ncsa.uiuc.edu. Many many thanks to him for all his hard work putting it together. Many more thanks also to Jonathan Haas, who began the tradition of posting the FAQ weekly. -- Matthew Daly I feel that if a person has problems communicating mwdaly@kodak.com the very least he can do is to shut up - Tom Lehrer My opinions are not necessarily those of my employer, of course. --- Support the anti-Spam amendment! Join at http://www.cauce.org ---