Possibly Wrong
possiblywrong.wordpress.com · Personal blog · on HN since 2013
A mathematically minded programmer writes about probability, puzzles, geometry and everyday calculations, such as Skittles duplicates and using a watch as a compass.
What HN saysHN commenters link it for its Skittles birthday paradox analysis, watch compass trick and blackjack posts, and the author joins the discussion himself.
17HN people shared it
7linked it in comments
13stories submitted
1.2Kstory points
5 months agolast shared
2013people per year2026
Most-shared posts
- 1I found two identical packs of Skittles among 468 packs3 people · 826 points · first shared 2019 · 207 comments on HN
- 2Calories in, calories out2 people · 193 points · first shared 2014 · 210 comments on HN
- 3Using a Watch as a Compass2 people · 2 points · first shared 2022 · discussion on HN
- 4Lemonade Stand1 people · 129 points · first shared 2024 · 42 comments on HN
- 5Analysis of adversarial binary search game1 people · 61 points · first shared 2024 · 14 comments on HN
- 6The Fisher-Yates shuffle is backward1 people · 5 points · first shared 2025 · 1 comments on HN
- 7If the Earth Were a Cube1 people · 4 points · first shared 2017 · discussion on HN
- 8String Art from Images1 people · 3 points · first shared 2022 · discussion on HN
- 9Floating-point equality: It’s worse than you think1 people · 2 points · first shared 2013 · discussion on HN
- 10Counting possible positions in the board game Battleship, regular and hexagonal1 people · 1 points · first shared 2016 · discussion on HN
- 11There Is No Equilux1 people · 1 points · first shared 2023 · discussion on HN
- 12Beware the "Natural" Quaternion1 people · 1 points · first shared 2026 · discussion on HN
- 13Homepage1 people · first shared 2015
- 14Identical packs of skittles1 people · first shared 2019
- 15Is the earth like a billiard ball or not1 people · first shared 2021
What HN people wrote when they linked it
possiblywrong · 2023-06-05
Author of the linked article here; re marking movement of shadows, I wrote a follow-up that discusses some alternatives, mainly that one:
https://possiblywrong.wordpress.com/2014/07/05/using-a-watch-or-a-stic…
jihadjihad · 2019-05-31
In a similar vein, I saw this linked from HN not too long ago and thought it was a really neat application of the birthday paradox--all about finding duplicate packs of Skittles: https://possiblywrong.wordpress.com/2019/04/06/follow-up-i-found-two-i…
Spectral · 2019-04-18
The picture he shows of all the Skittles' counts looks like something I would've seen at the local museum. He missed his chance of taking an ultra high resolution photo of it and putting it on display:
https://possiblywrong.wordpress.com/2019/04/06/follow-up-i-found-two-i…
scaramanga · 2015-03-31
Why? There are very efficient machine-learning-free solutions... There are even rote solutions a human can use n his own head with a bit of practice. The game is basically solved.
https://possiblywrong.wordpress.com/?s=blackjack
madcaptenor · 2024-01-17
You could probably make it in a few minutes - the direction of the sun is, to a first approximation, 15 degrees times the number of hours it is after midnight. This leads to a trick for using an analog watch as a compass:
https://www.citizenwatch-global.com/support/exterior/direction.html
https://www.watchaffinity.co.uk/blog/how-to-use-your-watch-as-a-compas…
This is more prone to errors closer to the equator and in the summer (https://possiblywrong.wordpress.com/2012/01/25/using-a-watch-as-a-comp… but should be good enough for picking a side of the bus.
(This is all in the northern hemisphere; in the southern hemisphere the sun goes the other way, so change the sign on everything.)
zokier · 2021-06-06
0.1mm is not very smooth. According to wikipedia, 150 grit sandpaper has average particle size of 90-100µm
edit: of course there is vigorous internet commentary about billiard ball smoothness compared to earth:
https://possiblywrong.wordpress.com/2011/01/03/is-the-earth-like-a-bil…
https://skeptics.stackexchange.com/questions/10763/is-earth-as-smooth-…
https://billiards.colostate.edu/faq/ball/smooth/
Which mostly seem to agree that earth definitely is not as smooth as a (new) billiards ball, but there is lots of debate about the details.
anonymousDan · 2015-03-14
I'm pretty sure there is some fundamental queueing theory to back this up, as it's the main takeaway I had from a queuing theory course I took in college. Can't remember the details though, so I'm not sure it would still apply if a single queue entailed long walks from the head of the queue to the nearest available 'processor'.
EDIT: more background here
https://possiblywrong.wordpress.com/2010/12/26/why-multiple-checkout-l…
It appears you might be right in practice.