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- Frequently Asked Questions (FAQS);faqs.297
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- umaxc.weeg.uiowa.edu 128.255.56.80 US -6 1990/05/15
- Organ: Univ. of Iowa
- Comment: 128.255.57.80
- Files: NCSA Telnet; Sendmail
-
- umd5.umd.edu 128.8.10.5 US -5 1990/05/15
- Organ: Univ. of Maryland
- Files: NeXT
-
- umigw.miami.edu 129.171.97.1 US -5 1990/05/15
-
- umn-cs.cs.umn.edu 128.101.224.1 US -6 1990/05/15
- Organ: Univ. of Minnesota
- Files: GNU; hypertext; news; Japanese
-
- umnstat.stat.umn.edu 128.101.51.1 US -5 1990/05/15
- Organ: Univ. od Minnesota
- Files: XlispStat; S Bayes
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- umrisca.isc.umr.edu 131.151.8.1 US -6 1990/05/16
-
- unibi.hrz.uni-bielefeld.de 129.70.4.128 DE +1 1991/09/30
-
- unidata.ucar.edu 128.117.140.3 US -7 1990/12/26
-
- uniwa.uwa.oz.au 130.95.128.1 AU ? 1991/09/30
- Files: RFC; Sendmail; GNU; Mac; network docs; Cnews; nn; Unix utils
-
- unix.secs.oakland.edu 141.210.180.2 US -5 1990/11/18
- Organ: Oakland Univ.
- Files: gcc; gas; gdb; and kermit for xenix
-
- unmvax.cs.unm.edu 129.24.16.1 US -7 1990/05/15
- Organ: Univ. of New Mexico
- Files: getmaps
-
- unx.ucc.okstate.edu 139.78.1.1 US -6 1991/02/23
- Organ: Oklahoma State Univ.
-
- uop.uop.edu 138.9.200.1 US -8 1990/08/22
- Files: Bnews; nn; IRC
-
- urth.acsu.buffalo.edu 128.205.7.9 US -5 1990/08/06
- Files: trn
-
- usc.edu 128.125.1.45 US -8 1991/01/17
- Organ: Univ. of Southern Cal
- Comment: 128.125.253.136
- Files: AMD (automounter); DECUS TECO
-
- utadnx.cc.utexas.edu 128.83.185.100 US -6 1990/08/22
- Organ: Univ. of Texas
- Files: VMS sources (zetaps; laser; sxlps)
-
- utnetw.utoledo.edu 131.183.1.1 US -5 1991/09/30
- Organ: Univ. of Toledo
- Files: VMSTPC
-
- utsun.s.u-tokyo.ac.jp 133.11.11.11 JP ? 1991/05/07
- Files: Japanese/Kanji software; Tron; GNU; info-mac; tex; X; network-related
- stuff
-
- uu.psi.com 136.161.128.3 US -5 1990/05/15
- Organ: PSI
- Files: GNU Emacs; others; Nysernet; IETF; GOSIP
-
- uvaarpa.virginia.edu 128.143.2.7 US -5 1990/06/04
- Files: u3g; whoisd; VERnet; uvapc; net docs/RFCs; misc net; etc.
-
- uvacs.cs.virginia.edu 128.143.8.29 US -5 1991/05/26
- Comment: 128.143.136.10
- Files: site techreports; Simple User Interface Toolkit (suit) - not the same as
- in X11R4; Mentat - parallel processing system
-
- uwasa.fi 128.214.12.3 FI +2 1990/12/23
- Organ: Univ. of Vaasa
-
- ux.acs.umn.edu 128.101.63.2 US -6 1990/05/15
- Organ: Univ. of Minnesota
-
- ux1.cso.uiuc.edu SEE: ftp.cso.uiuc.edu
-
- uxc.cso.uiuc.edu 128.174.5.50 US -6 1990/06/01
- Organ: Univ. of Illinois - Urbana-Champaign
- Files: games; HitchHiker's Guide to the Internet; recipes; GIF; GNU; RFC; IEN;
- and more
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- valeria.cs.ucla.edu 131.179.64.36 US -8 1991/11/28
- Organ: Univ. of California - LA (CS Dept)
- Files: info-zip; zip/unzip source
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- valhalla.ee.rochester.edu 128.151.160.11 US -5 1990/05/15
- Files: RFCs; Network load balancer
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- vax.cs.pitt.edu 130.49.2.1 US -5 1990/05/15
- Files: KA9Q
-
- vax.eedsp.gatech.edu 130.207.226.2 US -5 1991/05/26
- Organ: Georgia Tech
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- vax.ftp.com 128.127.2.100 US -5 1990/05/15
- Organ: FTP Software
- Files: FTP apps;
-
- vax1.cs.umass.edu 128.119.40.1 US -5 1990/08/22
- Organ: Univ. of Massachusetts
-
- vax1.umkc.edu 134.193.1.1 ? 1990/08/22
- Files: network info
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- vax2.cs.umass.edu 128.119.40.2 US -5 1990/08/22
- Organ: Univ. of Massachusetts
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- vela.acs.oakland.edu 141.210.10.2 US -5 1991/01/17
- Organ: Oakland Univ.
-
- venera.isi.edu 128.9.0.32 US -8 1990/05/15
- Files: statspy (NNstat); GNU Chess
-
- venus.eng.buffalo.edu 128.205.19.6 US -5 1992/02/23
- Admin: ghanem@venus.eng.buffalo.edu - Roger G. Ghanem
- Files: sysid apps for earthquake/structural dynamics in Fortran
-
- venus.ycc.yale.edu 130.132.1.5 US -5 1990/08/22
- Organ: Yale Univ.
- Files: SBTeX
-
- vernam.cs.uwm.edu 129.89.9.117 US -6 1992/09/26
- Organ: Univ. of Wisconsin - Milwaukee
- Files: 386BSD source & binaries; Suni386 binaries and mailing list; Mach386
- binaries
-
- vesta.sunquest.com 192.12.52.42 ? 1990/08/22
- Comment: 149.138.1.42
- Files: VMS cryptodisk and virtual disk driver
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- vlsi.cs.umn.edu 128.101.230.15 US -6 1990/08/22
- Organ: Univ. of Minnesota
- Files: PLP (Public line printer)
-
- vm.tcs.tulane.edu 129.81.128.1 ? 1990/08/22
- Files: RFC; terminfo
-
- vm.utdallas.edu 129.110.102.2 US -6 1990/08/22
- Files: lipphe IBM TCP/IP bit and drivers
-
- vm1.nodak.edu 134.129.111.1 US ? 1990/08/22
- Files: Minix fixes; EV1188 fixes; QNS; medical newsletter
-
- vmd.cso.uiuc.edu 128.174.5.98 1990/12/24
- ---> REMOVED 1992/09/10
-
- vms.ecs.rpi.edu 128.113.5.15 US -5 1990/08/22
- Organ: Rensselaer Polytechnic Institute
- Files: Message Exchange
-
- vms.huji.ac.il 128.139.4.3 IL +2 1991/09/30
-
- vms2.ecs.rpi.edu 128.113.5.14 US -5 1990/08/22
- Organ: Rensselaer Polytechnic Institute
- Files: NEWSRDR
-
- vmsa.oac.uci.edu 128.200.9.5 US -8 1991/02/21
- Organ: Univ. of California - Irvine
- Files: VMS make; TAR
-
- vmsa.technion.ac.il 132.68.1.40 IL +2 1991/09/30
-
- vmsd.oac.uci.edu 128.200.15.2 US -8 1990/08/22
- Organ: Univ. of California - Irvine
- Files: VMS stuff
-
- vmtecmex.cem.itesm.mx 132.254.1.4 MX ? 1991/02/08
- Files: Amiga; MSDOS; GIF
-
- walhalla.informatik.uni-dortmund.de 129.217.64.63 DE +1 1991/11/28
-
- watcgl.waterloo.edu 129.97.140.64 CA -5 1990/10/09
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- watmath.waterloo.edu 129.97.140.144 CA -5 1990/05/15
- Comment: 129.97.216.42
- Files: lots of stuff
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- watmsg.waterloo.edu 129.97.141.9 CA -5 1990/05/15
- Files: GNU; pd BSD; uSystem docs; virus; cryptography
-
- watnxt2.ucr.edu 192.31.146.189 US -8 1990/10/09
- Organ: Univ. of California - Riverside
-
- watserv1.uwaterloo.ca 129.97.129.140 CA -5/-4 1992/07/29
- Organ: Univ. of Waterloo
- Files: APL stuff in /languages/apl
-
- watserv1.waterloo.edu 129.97.129.140 CA -5 1990/08/22
-
- watsun.cc.columbia.edu 128.59.39.2 US -5 1990/05/15
- Organ: Columbia Univ.
- Files: kermit
-
- wayback.cs.cornell.edu 128.84.254.7 US -5 1991/04/24
- Organ: Cornell Univ.
-
- weedeater.math.yale.edu 130.132.23.17 US -5 1990/05/15
- Organ: Yale Univ.
- Files: rayshade; misc. raytracing goodies
-
- white.cerritos.edu 130.150.200.22 ? 1991/09/30
- Files: rec.motorcycles.pictures
-
- wilbur.stanford.edu 36.14.0.30 US -8 1990/12/26
- Organ: Stanford Univ.
-
- wilma.cs.brown.edu 128.148.31.66 US ? 1991/09/19
- Files: Brown CS Field and Thread packages; comp.robotics; XMX
-
- wlv.imsd.contel.com 192.26.147.1 US -5 1991/05/26
- Organ: Contel Corp
- Comment: 26.5.0.103
-
- wolfen.cc.uow.edu.au 130.130.68.4 AU ? 1991/01/17
-
- wowbagger.pc-labor.uni-bremen.de 134.102.228.9 DE +1 1992/06/29
- Organ: Univ. of Bremen
- Files: Amiga; Atari-ST; X11; TeX; neiral-nets; GNU (mirror of prep.ai.mit.edu)
-
- wpi.wpi.edu 130.215.24.1 US -5 1990/05/15
- Files: dspl; anime; fusion; Mac; GNU; ASH; DES; misc Unix; TeX_DS3100; TeX_Umax;
- misc X
-
- wsmr-simtel20.army.mil 192.88.110.20 US -7 1992/09/16
- Organ: U.S. Army - White Sands Missle Range
- Files: MSDOS; Unix; CPM; Mac (tenex)
-
- wuarchive.wustl.edu 128.252.135.4 US -6 1992/09/16
- Organ: Washington Univ.
- Comment: Open 24 hours
- Files: GNU; X.11R3; GIF; IEN; RFCs; TeX; UUPC; info-mac; 4.3BSD-Tahoe;
- comp.binaries: amiga, apple2, atari.st, ibm.pc; comp.sources: amiga, games,
- misc, sun, unix, x; msdos; Archives - SimTel20, cica (as mirrors/win3); Elm
-
- xanth.cs.odu.edu 128.82.8.1 US -5 1990/08/01
- Comment: 128.82.4.1, 128.82.4.65
- Files: comp.sources: games, misc, x, unix
-
- xanthorrhoea.maths.uwa.oz.au 130.95.16.13 AU ? 1991/09/26
-
- xcf.berkeley.edu SEE: scam.berkeley.edu
-
- xview.ucdavis.edu 128.120.1.150 US -8 1990/07/19
- Organ: Univ. of California - Davis
- Files: xview
-
- yalevm.ycc.yale.edu 130.132.1.4 US -5 1990/08/22
- Organ: Yale Univ.
-
- yallara.cs.rmit.oz.au 131.170.24.42 AU ? 1991/01/17
- Comment: 192.55.190.42
-
- ymir.claremont.edu 134.173.4.23 US -8 1990/08/22
- Organ: Claremont College
- Comment: 134.173.20.23, 134.173.21.23
- Files: lots of VMS; TeX-for-VMS; mainz fonts
-
- z.eecs.umich.edu SEE: ftp.eecs.umich.edu
-
- zaphod.lanl.gov 128.165.44.202 US -7 1991/02/23
-
- zaphod.ncsa.uiuc.edu 141.142.20.50 US -6 1990/08/13
- Organ: Univ. of Illinois - Urbana-Champaign
- Files: Mac X aaps; NCSA Telnet; Heirarchical Data File system; misc graphics &
- scientific formats
-
- zariski.harvard.edu 128.103.28.10 US -5 1990/05/15
- Organ: Harvard Univ.
- Files: macaulay
-
- zerkalo.harvard.edu 128.103.42.201 US -5 1990/05/15
- Organ: Harvard Univ.
- Files: traceroute
-
- zeus.cs.umu.se 130.239.32.12 SE +1 1991/11/28
- Comment: 130.239.80.2
-
- zeus.mgmt.purdue.edu 128.210.1.3 US -5 1990/05/15
- Organ: Purdue Univ.
-
- zeus.unomaha.edu 137.48.1.1 US -6 1991/02/21
- Organ: Univ. of Omaha
- Files: cedit - column editor
- Path: bloom-picayune.mit.edu!snorkelwacker.mit.edu!hri.com!spool.mu.edu!agate!usenet.ins.cwru.edu!magnus.acs.ohio-state.edu!csn!hellgate.utah.edu!hellgate!jacobs
- From: jacobs@cs.utah.edu (Steven R Jacobs)
- Newsgroups: rec.gambling,news.answers
- Subject: rec.gambling Changes to Frequently Asked Questions
- Date: 5 Oct 92 02:09:43 GMT
- Reply-To: jacobs@cs.utah.edu
- Followup-To: rec.gambling
- Organization: University of Utah CS Dept
- Lines: 110
-
- Approved: news-answers-request@MIT.Edu
- Expires: Fri, 13 Nov 1992 08:00:00 GMT
- Archive-name: gambling-faq/diff
- Comment: A blank line that was in the original posting above was
- deleted by the maintainer of the pit-manager.mit.edu FAQ
- archive, to bring the posting into a consistent format.
-
- Note: This "diff" file has been edited and is not intended for use by any
- automatic update software.
-
- ---
- > G10 What are some cheap places to stay in Vegas?
- ---
- > B14 Why are single deck games better than multi-deck games?
- ---
- > B23 What is the correct strategy for "multi action" blackjack?
-
-
- 513,514c516,517
- ---
- > Q:G10 What are some cheap places to stay in Vegas?
- > A:G10 (Ron Birnbaum)
- >
- > In response to those looking for nice but inexpensive accomodations in
- > Vegas, I can recommend two places:
- >
- > Downtown: The Ogden House - Fremont Street
- > I don't have their number, but some friends stayed there in
- > June for $18 per night, and found it clean and comfortable.
- > Their phone number is (702) 385-5200.
- >
- > Strip: King Alburt Motel
- > It's behind the Flamingo Hilton/Imperial Palace/Barbary Coast area.
- > Every unit is furnished with a kitchen, tv, and private bath, with
- > simple but clean furnishings. Their location is ideal, and they
- > quoted me day rates of $25/wk $40/wkend per night for a single.
- > And these prices were for March,('92) - usually a busy and high
- > priced season. And you can do even better than these rates for a
- > weekly rental. They are happy to negotiate! I don't believe they
- > have a toll-free number, but I'm not sure. Their regular number is
- > (702) 732- 1555
- >
- > Call the Las Vegas Tourism Beareau for details of other low-cost
- > area lodging. They have an toll-free number - 1-800-522-9555. Woops - I
- > just called it and they only handle casinos.
- >
- > But these 800 numbers DO handle the smaller places as well. I called the
- > LV Chamber of Commerece for these numbers, and they had even more than
- > these:
- >
- > 800 - 548-2008
- > 800 - 345-7177
- >
- > Through the 7177 number, I arranged a room in the beautiful new tower at
- > the Stardust for much lower than what the hotel quoted me directly, also
- > at a lower rate than the other 800 numbers could offer (32/wk 40/wkend).
- > They are a room 'wholesaler' and seem to be the best place to make
- > reservations through. The new tower at the Stardust is supposed to
- > be ****1/2, according to Julie - the agent I spoke with. She also asked
- > for a high floor which she said have spectatular views of the entire strip.
- >
- > They know all the deals in town! Good luck, hotel bargain hunters!!
- >
-
- 1138,1139c1185,1186
- ---
- > Q:B14 Why are single deck games better than multi-deck games?
- > A:B14 (Michael Hall)
- >
- > There are some surface differences, such as single and double deck usually
- > being hand-held, while four or more decks are dealt from a shoe, but there
- > are fundamental mathematical differences too.
- >
- > Single deck blackjack is usually better than multiple deck blackjack
- > for card counters, basic strategists, and the clueless. Additional decks
- > make busts less likely, since one can draw to hands like 2,2,2,2,2,2,2,2,2
- > (for 18) which are improbable/impossible in single deck. Busting less
- > often helps the dealer's hand more than yours, since the dealer is forced
- > by the rigid rules to hit more often than you. Blackjacks are also less
- > frequent, which is bad since you get paid 3 to 2 for those. All in all,
- > multiple decks will cost a basic strategist nearly 0.5% in advantage, which
- > is more than all but the very best package of favorable extra rules will
- > give you. This was an intuitive explanation; a complete mathematically
- > sound (albeit huge) proof can be generated by a combinatorial analysis
- > program.
- >
- > Card counters face the additional problem that the count is less volatile
- > with multiple decks and hence offers less frequent opportunities for large
- > favorable bets. Consider the difference between an urn with 1 black and
- > 1 white marble versus an urn with 100 black and 100 white marbles. Draw
- > half the marbles: what is the probability that all the remaining marbles
- > are white? In the 1 and 1 case, there is a 1 in 2 chance. In the 100 and
- > 100 case, there is only a 1 in 100,891,344,545,564,193,334,812,497,256
- > chance!
- >
- >
-
- 1392,1393c1469,1470
- > Q:B23 What is the correct strategy for "multi action" blackjack?
- > A:B23 (Steve Jacobs)
- >
- > Multi Action blackjack allows the player to place up to three bets
- > simultaneously on the same blackjack hand. The player is dealt a
- > single hand, and the three bets are played out against the same dealer
- > upcard, but with different "drawn" cards for each bet. Many players
- > feel nervous about hitting stiff hands against a high dealer's upcard
- > (7 or higher), since they will lose all three bets if they bust.
- > However, basic strategy is COMPLETELY UNCHANGED for this game, and the
- > correct strategy is no different than if the player had only a single
- > bet at risk.
- >
- --
- Steve Jacobs ({bellcore,hplabs,uunet}!utah-cs!jacobs, jacobs@cs.utah.edu)
- "Be afraid. Be very afraid. I have K-10 offsuit...."
- Xref: bloom-picayune.mit.edu rec.gambling:12274 news.answers:3399
- Newsgroups: rec.gambling,news.answers
- Path: bloom-picayune.mit.edu!snorkelwacker.mit.edu!news.media.mit.edu!micro-heart-of-gold.mit.edu!wupost!zaphod.mps.ohio-state.edu!caen!hellgate.utah.edu!cs.utah.edu!jacobs
- From: jacobs@cs.utah.edu (Steve Jacobs)
- Subject: rec.gambling Frequently Asked Questions
- Date: 8 Oct 92 10:45:24 MDT
- Message-ID: <1992Oct8.104525.13806@hellgate.utah.edu>
- Followup-To: rec.gambling
- Lines: 2470
- Reply-To: jacobs@cs.utah.edu
- Approved: news-answers-request@MIT.Edu
- Expires: Fri, 13 Nov 1992 08:00:00 GMT
-
- Archive-name: gambling-faq/part1
-
- ==================================
- This is the rec.gambling Frequently Asked Questions (FAQ) list.
-
- I wish to thank Frank Irwin for helping to compile much of the information
- that appears in this list. I also wish to thank those who contributed
- information, as well as those who spent countless hours running blackjack
- simulations in order to help answer many of these questions. Changes or
- additions to this FAQ list should be submitted to: jacobs@cs.utah.edu
-
- ==================================
- Table of Contents
-
- Section S: Spare us!
- S1 Martingale betting systems -- just double your bet until you win
- S2 The Inevitable Monty Hall
- S3 How much would you pay to play this game?
-
- Section G: General Gambling Topics
- G1 What's in it for me? (Why read rec.gambling)
- G2 Where can I get books about gambling?
- G3 Is there a gambling archive?
- G4 How do you get comps?
- G5 What comps are available?
- G6 How do I get a casino credit line?
- G7 How are "markers" used?
- G8 What are the phone numbers for hotels/casinos in Las Vegas?
- G9 What are some good places to play/stay in Reno?
- G10 What are some cheap places to stay in Vegas?
- G11 Where can I get casino quality chips?
- G12 What are matchplay chips
- G14 Is this Vegas World offer worth it?
- G15 When did rec.gambling get started?
-
- Section B: Blackjack
- B1 What do these funny acronyms mean ...
- B2 What special terminology is used by blackjack players?
- B3 What special terminology is used by card counters?
- B4 What are "pit critters"?
- B5 Why is there so much talk about blackjack in rec.gambling?
- B6 Is casino blackjack a "beatable" game.
- B7 How much of an advantage can card counting give?
- B8 Is card counting illegal?
- B9 Can the casino ban card counters?
- B10 What is the correct basic strategy for single deck Blackjack?
- B11 What is the correct basic strategy for Atlantic City blackjack?
- B12 What is the house edge when playing basic strategy?
- B14 Why are single deck games better than multi-deck games?
- B15 Do 'bad' players at third base have any effect on expected gain?
- B16 Where is the best place to sit at a blackjack table.
- B17 How is card counting done?
- B18 What counting system is "best"?
- B19 What counting system is easiest to use?
- B20 What BJ counting system is most effective?
- B21 Does penetration have any effect on basic strategy expectation?
- B22 What is the correct strategy for late surrender?
- B23 What is the correct strategy for "multi action" blackjack?
- B24 What is "Over/Under" Blackjack?
- B26 What is the counting strategy for Over/Under blackjack?
- B26 What are some good/bad books on Blackjack?
- B27 What are some other sources of blackjack/gambling information?
-
- Section C: Craps
- C1 What special terminology is used at the Craps table?
- C2 How is Craps played?
- C3 What are "Odds?"
- C4 What are "Come" and "Don't Come" bets?
- C5 What are all those other bets?
-
- Section V: Video Poker
- V1 Is it possible to gain an advantage at Video Poker?
- V2 What is the "basic strategy" for Video Poker?
-
- Section P: Poker
- P1 How is Texas Hold'em played?
-
- Section M: Miscellaneous
- M1 How is Baccarat played?
- M2 How is Red Dog played?
- M3 Can the lottery be beat when the jackpot gets high enough?
- M4 How is Pai Gow Poker played?
- M5 Is there a horse racing newsgroup?
-
- ==================================
- Section S: Spare us!
-
- These questions come up occasionally, causing a lot of heated discussions
- and wasted bandwidth. The rec.gambling regulars are pretty sick of seeing
- these questions, and they would appreciate it if you just didn't ask them.
- If you do ask, we'll probably just say "see the FAQ list".
-
- Q:S1 Martingale betting systems -- just double your bet until you win
- A:S1 (Frank Irwin, Steve Jacobs)
-
- From: "The Eudaemonic Pie" by Thomas A. Bass
-
- The word comes from the French expression "porter les chausses a la
- martingale," which means "to wear one's pants like the natives of
- Martigue," a village in Provence where trousers are fastened at the
- rear. The expression implies that this style of dress and method of
- betting are equally ridiculous.
-
- The betting scheme merely states that you would want to double your
- bet after each loss. Beginning with one unit, you would bet two units
- if you lost the first. Then four, then eight, until you win a bet. You
- would then revert to a one unit bet. The theory is that with each win
- you will win all that you lost since the last win, plus one unit. The
- reality is that you will quickly come to a betting ceiling, governed by
- either your bankroll or the house limit, above which you may not increase
- your bet. After 9 straight losses (it's happened to me) you would be
- betting 512 units.
-
- In practice, a lot of people get sucked into betting this way because it
- gives the illusion of really working. This is because most of the time,
- you will end a string of bets with a win. However, on those rare occasions
- when you do lose, you will lose a lot of money. So, the end result is that
- you win a small amount almost always, but when you lose you will lose more
- than all of your little wins combined.
-
- The important point to realize is that most games simply cannot be beat
- in the long run. In games such as craps, roulette, and non-progressive
- slot machines, it is mathematically impossible to gain an advantage over
- the house.
-
-
- Q:S2 The Inevitable Monty Hall
- A:S2 (Steve Jacobs)
-
- You are a contestant on "Let's Make A Deal", and Monty Hall offers you
- your choice of three doors. One door has a prize, and the other two
- doors are empty. Monty knows in advance where the prize is, and no
- matter which door you pick, Monty will open one of the other doors to
- show you that it is empty. Monty then offers to allow you to trade your
- door for the other unopened door. What should you do?
-
- My best advice is to grab Monty around the neck and strangle him :-)
-
- The short answer is that you should switch doors, because it increases
- your chance of winning from 1/3 to 2/3. The odds are not 50/50, because
- the probability that the prize is behind the door you originally picked
- is 1/3, and this probability never changes until the prize is revealed.
- This can be seen by considering what happens if you decide to *never*
- switch doors -- in this case you will win one time in three, since you
- will win only if your original pick is correct. So, if you *always*
- switch you will win 2/3 of the time, since you win whenever your original
- pick was wrong. Since Monty can (and will) always show an empty door, it
- is as if he is saying "you can keep your door, or you can trade is for
- BOTH of the other doors, and to confuse you I will show you that one of
- the other doors is empty, even though you already knew that".
-
- Some of you won't believe that this is correct. You will say "after Monty
- opens a door, there are only two choices so you have an equal chance of
- winning whether you switch or not". This is wrong. The fact that there
- are only two choices does NOT imply that the two choices have equal
- probability. Still not convinced? Suppose there are 100 doors, and only
- one prize. You pick a door, and Monty shows you 98 empty doors (he can
- always do this, since he knows where the prize is), and offers to let you
- switch. The chance that your original pick was right is 1/100. If you
- never switch, you will almost always lose. Therefore, if you always switch
- you will almost always win.
-
- Not convinced? Try it yourself, but try playing the role of Monty in order
- to help see how it works. Don't ask rec.gambling, because we'll know you
- didn't really try it yourself.
-
- The confusion caused by this question shows that probability problems
- often go against human intuition. This question appeared (several times)
- in the "Ask Marilyn" column of the "Parade" insert that appears in many
- Sunday newspapers in the United States. Many people with Ph.D.'s in
- mathematics claimed in wild disbelief that Marilyn's answer [2/3] was
- wrong, and that it was a sad commentary on the American education system.
- Indeed it is, because the mathematicians were wrong.
-
-
- Q:S3 How much would you pay to play this game?
- A:S3 (John P. Nelson)
-
- >I flip a coin until it comes up tails. If it comes up tails the first
- >time, you get $2; if the second, $4; if the third time, $8. That is,
- >if I flip the coin N times, you get 2^N bucks. [How much would you
- >pay to play this game?]
-
- The problem is, of course, that the "expected value" of this game is an
- infinite series that does not converge: The "expected" win appears to
- be infinite. However, in any REAL implementation of this game, there
- would have to be an upper limit to your liability: It would be
- unreasonable to expect you to really pay off a win of trillions of
- dollars.
-
- If you put an upper limit on the number of flips, then the expected
- value of the game converges, and it is quite easy to calculate the
- "break even" wager. If we limit the game to N flips, and you pay me
- $2^M if tails comes up on the M'th flip and if N flips occur with no
- tails, you pay me 2^(N+1), then the expected value of each game is
- simply N+2. (A variation on the rules: If you pay me 0 if N flips
- occur with no tails, then the expected value of the game is $N).
-
- This is fairly easy to calculate: On each independent trial, the
- chance of a tails is 1/2. Clearly, the chance of a tails on the
- second trial is 1/4 (1/2 chance of heads on the first trial, times
- 1/2 chance of tails on the second trial). The odds of a tail occuring
- on the Nth flip is 1/(2^N). The payoff at that point is 2^N. So we
- have the series:
-
- 1/2 * payoff-1flip + 1/4 * payoff-2flip + 1/8 * payoff-3flip
-
- or:
-
- $2 $4 $8 $(2^N)
- -- + -- + -- ... ------
- 2 4 8 $(2^N).
-
- Given a maximum of N flips, the expected win is 1+1+1..., N times.
- Given a $0 payoff on N heads in a row, that is the total expected win:
- N. If you pay off 2^(N+1) after N tails, the final term is
-
- $(2^(N+1))
- ---------- = 2
- $(2^N)
-
- Which explains where the +2 in (N+2) comes from.
-
-
- ==================================
-