4 ms·
Here's a similar puzzle that can be used as a fun bar trick: Given a standard deck of 52 cards, a third party chooses any five from the deck and hands them to
by martingordon 12y ago
Here's a similar puzzle that can be used as a fun bar trick:
Given a standard deck of 52 cards, a third party chooses any five from the deck and hands them to your accomplice. Your accomplice chooses four of the five and gives them to you, with which you identify the fifth card. What's the strategy?
Solution (In Rot-13, http://rot13.com/index.php http://rot13.com/index.php):
N fvzcyr beqrevat bs sbhe pneqf qbrfa'g jbex, fvapr 4! bayl nssbeqf lbh 24 pbzovangvbaf (cyhf gur sbhe lbh unir).
Jvgu svir pneqf naq bayl sbhe fhvgf, lbh xabj bar bs gur fhvgf zvtug or qhcyvpngrq. Lbh pna hfr gur svefg pneq gb fhccyl bayl fhvg vasbezngvba, ohg gur erznvavat guerr pneqf bayl nssbeq 6 pbzovangvbaf (cyhf 1-4 vs lbh unccra gb qenj pneqf zngpuvat gur gnetrg'f fhvg).
Gur frperg vf gb pubbfr juvpu bs gur gjb pneqf gb unaq bire. Jvgu 13 pneqf va rnpu fhvg, gur znkvzhz qvfgnapr orgjrra nal gjb pneqf (nyybjvat sbe jenc nebhaq) vf 6. Ol nterrvat gb nyjnlf unaq bire gur fznyyre/ynetre bs gur gjb pneqf va gur fnzr fhvg nf lbhe fhvg vqragvsvre, lbh pna hfr gur erznvavat guerr gb vaqvpngr gur qvfgnapr hc/qbja sebz gung pneq.
Sbe rknzcyr, tvira:
3,5 Pyhof, 8 Fcnqrf, 10 Qvnzbaqf, X Urnegf
Qhcyvpngr fhvg vf pyhof, fb jr'yy unaq bire gur fznyyre bs gur gjb (3 Pyhof). Gur qvfgnapr orgjrra 3 naq 5 vf 2, fb jr unaq bire gur gur erznvavat guerr va gur frpbaq ybjrfg beqrevat bs gur pneqf (v.r., 132: 8 Fcnqrf, X Urnegf, 10 Qvnzbaqf).
- kevan 12y agoAvpr gb frr gur Cvtrbaubyr cevapvcyr va npgvba gurer.
- stumacd 12y agoJbhyq lbh nyfb arrq gb nffvta gur fhvgf n 'fgeratgu' va gur rirag gung gur svany 3 funerq n ahzore? Va lbhe rknzcyr, ubj jbhyq lbh jbex bhg gur qvfgnapr vs gur 3 pneqf gung lbhe sevraq tnir lbh jrer gur xvatf bs urnegf, qvnzbaqf naq fcnqrf?
- martingordon 12y agoYes, that's correct. I thought I had that in the post but it may have just been a draft version. I use nycunorgvpny because it's easy to remember.
- Kiro 12y agoWhat is this trick called?
- kevlened 12y ago"The best card trick" http://mathoverflow.net/questions/9754/magic-trick-based-on-deep-mathematics/9914#9914 http://mathoverflow.net/questions/9754/magic-trick-based-on-...
- Guillaume86 12y agoV guvax V zvffrq fbzrguvat, ubj qb lbh xabj vs lbh unir gb nqq be fhofgenpg gur qvssrerapr? Sbe rkrzcyr: 3,X Pyhof, 8 Fcnqrf, 10 Qvnzbaqf, X Urnegf Fb V erzbir "3 Pyhof" naq qvssrerapr vf 3 (fb V beqre gur erznvavat pneqf va gur guveq beqrevat beqre 213) ohg +3 naq -3 obgu tvir n ybjre inyhr guna X (3 be 10).
- sesqu 12y agoNqqvat be fhofgenpgvat jnf cer-neenatrq. Sbe 3,X gur ybjre bs gur gjb vf pbashfvatyl X.
- philh 12y agoVf lbhe nppbzcyvpr nyybjrq gb beqre gur pneqf gurl unaq lbh va gur jnl gurl pubbfr? Vs abg, guvf frrzf yvxr vg fubhyq or vzcbffvoyr: gurer ner (52 pubbfr 5) frgf gung gur guveq cnegl pna pubbfr, naq bayl (52 pubbfr 4) frgf gung lbh pna or tvira, fb ol gur cvtrbaubyr cevapvcyr, lbh pna'g znc rirel 4-frg gb n havdhr 5-frg. Ohg lbh pna znc na beqrerq 4-frg gb na habeqrerq 5-frg. Ohg V serdhragyl svaq gung zl cebbsf bs vzcbffvovyvgl ba guvatf yvxr guvf ner jebat, fb...
- martingordon 12y agoYes, they're allowed to/required to do that. Otherwise, I agree with you that it would be impossible.
- jammaloo 12y agoCbffvoyl bhgfvqr bs gur fcvevg bs gur chmmyr, ohg lbh pbhyq rapbqr gur qngn ol hfvat pneq bevragngvba naq jung unaq vf hfrq gb cnff vg. Vs V cnff lbh n pneq snpr hc, gura gung vf 01, snpr qbja vf 00. Vs V cnff vg gb lbh jvgu zl evtug unaq, gung'f 10, yrsg unaq vf 00. 4^4, vf 256 ovgf bs qngn gb jbex jvgu.