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Two envelopes problem

en.wikipedia.org Reference Encyclopedia entries Mathematics & science Class of 2022-05 Hall of Fame
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Resurfaced independently across 7 calendar years, with breakout response in 2 of them.

submissions
7
submitters
6
observed span
2010–2025
peak thread · 300 comments
249 pts
latest 20+ return · 2022-05-30
249 pts

Submission timeline

2007–2026

One slot for every year since HN launched. Height is that year's peak points; orange marks a 100+ point or 50+ comment breakout. Select a bar to open its strongest thread.

First comments on top threads

HN comment order

A simple non-mathematical resolution is that no information has been gained by selecting the first envelope. Since no information about the contents was available before selecting the first envelope switching envelopes is a neutral act. While this sounds like just a lazy intuitive explanation, it calls out the key component - a lack of information about the outcome - that can help avoid the paradox in more complex situations. This is in contrast to the three-door problem where information is…

kloch·249-point thread·

Isn't the expected value of both envelopes, prior to picking either, 0.5 * X, where X is the sum of the envelopes' value? So one way to argue this is a fallacious problem is that you can't take an unknown (the actual value of the envelope that you picked) and pretend it's a known. The value of the envelope you are holding, prior to opening it, is 0.5 * X. The value of the other envelope is also (0.5 *…

Since no information is gained between one's first choice and the second, I see no advantage in changing. In that sense, this problem differs from the Monty Hall problem, wherein new information is revealed between the first and second choice.

The first top-level comment from each of the four biggest threads, in HN’s own order. Excerpts are shortened; open a comment for full context.

Breakout years
2

100+ points or 50+ comments

Total points
376

reference only — not used in Hall rules or ranking

Total comments
390

reference only — not used in Hall rules or ranking

Every submission

DateTitle as submittedByPointsComments
2010-08-06Two Envelopes ProblemFirst breakoutatomon11288
2013-03-05Two envelopes paradoxsimonster20
2014-10-01The Two Envelopes ProblemGupie10
2020-01-23Two Envelopes Problemminouye20
2022-05-30Two envelopes problemHall induction · Best thread · Latest 20+ point returnniklasbuschmann249300
2024-04-04Two Envelopes ProblemEndXA20
2025-07-02Two Envelopes Problematomon82