Geekzone: technology news, blogs, forums
Guest
Welcome Guest.
You haven't logged in yet. If you don't have an account you can register now.


Forums › Off topic › Someone with a Masters degree in reasoning and logic please help me
Batman

Mad Scientist
30014 posts

Uber Geek
+1 received by user: 6217

Trusted
Lifetime subscriber

#171343 14-Apr-2015 16:53
Send private message



I don't get it.

1) 2 separate persons got told each the month, the other the day of a birthday.

2) A states he doesn't know the birthday but he is sure B doesn't know.

3) B says he knows the birthday.

4) A deduces if B knows then A must know it too.

WTF

View this topic in a long page with up to 500 replies per page Create new topic

This is a filtered page: currently showing replies marked as answers. Click here to see full discussion.

kendo
213 posts

Master Geek
+1 received by user: 26


  #1283069 14-Apr-2015 17:06
Send private message

Judging by the poor grammar I think it was either translated incorrectly or made up with no real answer.



NonprayingMantis
6434 posts

Uber Geek
+1 received by user: 1528


  #1283077 14-Apr-2015 17:17
Send private message

think about the reverse logic and the list of potential answers.

If Albert states he doesn't know, but that he also knows that Bernard doesn't know,  then that narrows down the list for Bernard to consider

say, for example, the date was 19th May.  If bernard had been told  "it's the19th", then he would know the answer was 19th May.
So for Albert, who only knows the month, to confidently state Bernard doesn't know,  Albert MUST know the month is one of the months that doesn't contain a unique number.  (if it wasn't, he couldn't be sure Bernard didn't know) therefore it can't be June or May.  and so must be July or August.

Bernard initially doesn't know, but when Albert states that he knows Bernard doesn't know,  then Bernard knows that the correct month must be one without a unique date. (July or August).  That is the only way for Albert to correctly state that he knows Bernard doesn't know.

So now Bernard knows's that it must be July or August. For him to state that he now knows the answer, it MUST be one of the dates that doesn't appear in both July and August, i.e. 16th, 15th, or 17th.  Since there are two options (15th 17th) for august, but only 1 for July (16ht), for him to state he now knows the correct month, it MUST be July.

so the answer is 16th July.  It's the only date option for which these statements can all be correct.

View this topic in a long page with up to 500 replies per page Create new topic








Geekzone Live »

Try automatic live updates from Geekzone directly in your browser, without refreshing the page, with Geekzone Live now.


Updates »

Are you subscribed to our RSS feed? You can download the latest headlines and summaries from our stories directly to your computer or smartphone by using a feed reader.








RSS feeds
Main feed
Forums feed
Copyright
©2002-2026 Geekzone®
Site features
Geekzone BI dashboard
Geekzone Badges
Geekzone Status Page

 

Site Information
Subscribe to Geekzone
Privacy Statement
Forum Usage Guidelines (FUG)
Advertising
Trademark and copyright