Someone with a Masters degree in reasoning and logic please help me

✨ Quic broadband | Samsung | AliExpress | Wise | Sharesies | GoodSync | Free white papers

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
29771 posts

Uber Geek

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

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

kendo

213 posts

Master Geek

#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

#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.

News and reviews »

Gen Threat Report Reveals Rise in Crypto, Sextortion and Tech Support Scams
Posted 7-Aug-2025 13:09

Logitech G and McLaren Racing Sign New, Expanded Multi-Year Partnership
Posted 7-Aug-2025 13:00

A Third of New Zealanders Fall for Online Scams Says Trend Micro
Posted 7-Aug-2025 12:43

OPPO Releases Its Most Stylish and Compact Smartwatch Yet, the Watch X2 Mini.
Posted 7-Aug-2025 12:37

Epson Launches New High-End EH-LS9000B Home Theatre Laser Projector
Posted 7-Aug-2025 12:34

Air New Zealand Starts AI adoption with OpenAI
Posted 24-Jul-2025 16:00

eero Pro 7 Review
Posted 23-Jul-2025 12:07

BeeStation Plus Review
Posted 21-Jul-2025 14:21

eero Unveils New Wi-Fi 7 Products in New Zealand
Posted 21-Jul-2025 00:01

WiZ Introduces HDMI Sync Box and other Light Devices
Posted 20-Jul-2025 17:32

RedShield Enhances DDoS and Bot Attack Protection
Posted 20-Jul-2025 17:26

Seagate Ships 30TB Drives
Posted 17-Jul-2025 11:24

Oclean AirPump A10 Water Flosser Review
Posted 13-Jul-2025 11:05

Samsung Galaxy Z Fold7: Raising the Bar for Smartphones
Posted 10-Jul-2025 02:01

Samsung Galaxy Z Flip7 Brings New Edge-To-Edge FlexWindow
Posted 10-Jul-2025 02:01

Geekzone Live »

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

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: ©2002-2025 Geekzone®

Site features: Geekzone BI dashboard; Geekzone Badges; Geekzone Status Page

Affiliate links: Samsung; AliExpress; Wise; Sharesies; GoodSync

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