Difficult riddle about impatient people

  • Context: Undergrad 
  • Thread starter Thread starter americanpsy
  • Start date Start date
  • Tags Tags
    Riddle
Click For Summary

Discussion Overview

The discussion revolves around a riddle involving two impatient people who agree to meet between 3pm and 4pm, with the stipulation that they will only wait for 15 minutes. Participants explore the probability of them actually meeting given their constraints and assumptions about arrival times.

Discussion Character

  • Exploratory, Mathematical reasoning, Debate/contested

Main Points Raised

  • Some participants assert that no one will arrive before 3pm or after 4pm, establishing a clear timeframe for the meeting.
  • One participant suggests that if it is common knowledge that they will not arrive before 3:15pm, the probability of meeting can be calculated as 1/2 if only one person adopts this strategy.
  • Another viewpoint proposes that if both individuals arrive randomly between 3:15 and 3:45, the probability of them meeting increases to 3/4.
  • A later reply posits that if both individuals are aware of each other's reasoning and arrive around 3:30, the probability of meeting becomes 1.

Areas of Agreement / Disagreement

Participants present multiple competing views regarding the probability of meeting, with no consensus reached on a definitive answer.

Contextual Notes

The discussion relies on assumptions about common knowledge and rational behavior of the participants, which may not be universally applicable. The mathematical steps leading to the probabilities are not fully resolved.

Who May Find This Useful

Individuals interested in probability theory, game theory, or those who enjoy logical puzzles may find this discussion engaging.

americanpsy
Messages
3
Reaction score
0
Two impatient people agree to meet up sometime between 3pm and 4 pm, in the era before mobile phones, just near Nelson's Column in London. They are so impatient they will only wait 15 minutes before leaving. What is the probability they actually meet up?
 
Mathematics news on Phys.org
Supposing nobody will arrive before 3pm or after 4pm...
7/16
:smile:
 
Yes that is the assumption. No arrivals before 3pm or after 4pm.
 
An easy way to understand the answer...
 

Attachments

  • prob_meet.png
    prob_meet.png
    2 KB · Views: 732
If it is common knowledge that they will not arrive before 3 pm or after 4 pm, and wait for 15 minutes, they can do better: It is not necessary to show up before 3:15 - the other one will not have left before that. In the same way, it is not necessary to be there after 4 pm. Assuming that just one of them comes to that conclusion and the other one arrives at a random time, you can get a meeting probability of 1/2.
If both come to that conclusion, but choose a random arrival time between 3:15 and 3:45, their meeting probability is 3/4.
If they both know that the other one will do this analysis, they are both there around 3:30 and the meeting probability is 1.
 

Similar threads

  • · Replies 2 ·
Replies
2
Views
2K
Replies
8
Views
7K
  • · Replies 8 ·
Replies
8
Views
4K
  • · Replies 14 ·
Replies
14
Views
3K
  • · Replies 3 ·
Replies
3
Views
2K
Replies
5
Views
2K
  • · Replies 13 ·
Replies
13
Views
6K
  • · Replies 4 ·
Replies
4
Views
1K
  • · Replies 6 ·
Replies
6
Views
4K
  • Poll Poll
  • · Replies 9 ·
Replies
9
Views
3K