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        riddles >> medium >> WILLYWUTANG  & TWO CONDOMS
        
(Message started by: atgdax on Nov 22^nd, 2006, 6:47am)

Title: WILLYWUTANG & TWO CONDOMS
Post by atgdax on Nov 22^nd, 2006, 6:47am

how is the 2 condoms 3 women possible ?

and as far as i can tell, in the WILLYWUTANG question- if it is corret 93% then P = 93% .
could it be that easy or am i missing somthing ?

Title: Re: WILLYWUTANG & TWO CONDOMS
Post by towr on Nov 22^nd, 2006, 7:13am

http://www.ocf.berkeley.edu/~wwu/cgi-bin/yabb/YaBB.cgi?board=riddles_easy;action=display;num=1129750094;

Title: Re: WILLYWUTANG & TWO CONDOMS
Post by towr on Nov 22^nd, 2006, 7:17am

on 11/22/06 at 06:47:27, atgdax wrote:

and as far as i can tell, in the WILLYWUTANG question- if it is correct 93% then P = 93% .
could it be that easy or am i missing somthing ?

You're neglecting the prior probability of 0.001. In the other 0.999 cases the test still gives 93% wrong answer (i.e. saying they're ill when they're not)

Title: Re: WILLYWUTANG & TWO CONDOMS
Post by Icarus on Nov 22^nd, 2006, 7:28am

You will find the 2 condoms puzzle in the easy section, and several threads where you can find the answer in the easy forum.

There are also threads for the medium puzzle ("Willywutang has STDs? (http://www.ocf.berkeley.edu/~wwu/riddles/medium.shtml#willywutangHasSTDs)") wherein you will discover that the 93% value is not correct. Note that the statistics given say that if the person has an STD, 93% of the time the test will come out positive. But the question asked is: if the test comes out positive, what is the probability the person has an STD? This reversing has a profound effect on the probability - particularly given the low likelyhood of having an STD in the first place.

One other thing: We don't have access to know what it is you have been reading. When you post without fully explaining what you are refering to, it makes it extremely difficult for anyone else to have any idea what you are talking about. It took some work on my part to figure out what you meant by the "the WILLYWUTANG question" (willywutang appears in several puzzles here - it's a nickname of the sites creator William Wu).

Please, when posting in reply to a riddle-page riddle, either quote the riddle in the first post, or link to it, so others will know what you are refering to.