explain xkcd - User contributions [en]

464: RBA

2025-01-03T18:56:04Z

162.158.42.157: /* Explanation */

{{comic
| number = 464
| date = August 18, 2008
| title = RBA
| image = rba.png
| titletext = This is a story all about how I started drinking.
}}

==Explanation==
A [http://www.urbandictionary.com/define.php?term=Bel%20Air Bel-Air] is an internet meme where a poster on a message board starts a post on a serious topic, but partway through the post switches to reciting the lyrics to the opening theme song of ''{{w|The Fresh Prince of Bel-Air}}'', a 1990s sitcom starring {{w|Will Smith}} (previously known in his rapping career as the "Fresh Prince") as a street-smart teenager from West Philadelphia who has been sent to live with his affluent and stuffy Aunt and Uncle in Bel Air, Los Angeles by his mother as a consequence of a single altercation with a couple of no-good guys who were making trouble in his previous neighbourhood.

[[Megan]] in the comic reverses the traditional arrangement by starting the conversation with a recitation of the lyrics to said theme song, and then switching partway through to a very serious discussion of the status of their relationship culminating in a break-up.

The lyrics go like this:

:Now this is the story all about how
:My life got flipped, turned upside down
:And I'd like to take a minute just sit right there
:I'll tell you how I became ''the prince of a town called Bel-air''

The title ''RBA'' is an acronym for ''Reverse Bel-Air''.

The title text is also an RBA, but one that diverges from the song lyrics much more quickly. It's a play on the phrase "started drinking." This phrase usually refers to someone becoming an alcoholic (in this case, it would be because of the break-up), but in this case refers to the actual fact that Cueball had just started drinking (likely a glass of water) when Megan started talking to him.

A similar (though less serious) play on the Bel-Air meme was later used in [[1059: Bel-Air]].

==Transcript==
:[Megan walks up to Cueball pouring himself a drink.]
:Megan: Now, this is a story all about how

:Megan: My life got flipped turned upside down

:Megan: And I'd like to take a minute
:Megan: Just sit right there

:Megan: I'll tell you how I became uncertain about our relationship. I think you just like having a girlfriend, it doesn't matter who.
:Megan: I think we should break up.

:The reverse Bel-Air only works once, so make it something unforgettable.
:[Cut to a dropped glass, the drink spilled on the ground.]
:Cueball: ...wait, seriously?
:Megan: Yeah.

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Songs]]
[[Category:Fiction]]

Talk:3024: METAR

2024-12-14T16:51:38Z

162.158.42.157:

OMG RANDALL ADDED AN AO3 REFERENCE '''[[User:42.book.addict|42.book.addict]][[User talk:42.book.addict|Talk to me!]]''' 19:43, 13 December 2024 (UTC)
:must've been reading the fic of bill [[User:CalibansCreations|'''Caliban''']] ([[User talk:CalibansCreations|talk]]) 21:04, 13 December 2024 (UTC)
I love the things I learn from these things[[User:Rustykid52|Rustykid52]] ([[User talk:Rustykid52|talk]]) 19:48, 13 December 2024 (UTC)

Was the explanation of wind speed written by a European? The punctuation after "18" is a comma, not a period, so they it means over 18 thousand knots. [[User:Barmar|Barmar]] ([[User talk:Barmar|talk]]) 19:59, 13 December 2024 (UTC)
: Yes, it was. I'm sorry. [[User:Janfred|Janfred]] ([[User talk:Janfred|talk]])
: If windspeed interpreted at "european style", i.e. 18 and 35/1000 knots, it s still funny, beacouse such precision of wind speed measurement is 1] unreachable (variability at space & time is several horders higher), 2] useless (fraction of knot make no difference for pilots). ([[HonzaM])

"38.08 inches of mercury" seems a very high pressure, even for a station that is well below sea level. (1290 hPa Pressure around the dead sea is typically 1060hPa).. Is that physically realistic, or is it part of the joke? I know funnel clouds, freezing and volcanic ash in the same location are unlikely outside of the apocalypse, but can be justified by the rule of funny. [[Special:Contributions/172.70.160.135|172.70.160.135]] 20:11, 13 December 2024 (UTC)
:Indeed, 31.80 is the reference high limit. Still, is Randall a pilot? The structure of a METAR is horribly familiar to us pilots but pretty much a blank stare to anyone else. [[Special:Contributions/172.68.245.25|172.68.245.25]] 21:03, 13 December 2024 (UTC)
:Feeding it into a [https://www.weather.gov/epz/wxcalc_pressurealtitude calculator] gives an altitude of -2080m (-6825'). So it's entirely reasonable as long as your weather station is in a deep mine. [[User:BunsenH|BunsenH]] ([[User talk:BunsenH|talk]]) 21:08, 13 December 2024 (UTC)
:: But isn't the value always put in reference to MSL? I.e. I'm at an airport at 1000ft, the pressure reads 977 hPa, but I'll put 1013 hPa in the METAR. (QNH in METAR vs QFE at the station) [[User:Janfred|Janfred]] ([[User talk:Janfred|talk]]) 21:14, 13 December 2024 (UTC)
::: There may be various complicated pressure differences from the tornado having dumped a load of possibly Iclandic pyroclastic tephra upon the station. [[Special:Contributions/141.101.98.181|141.101.98.181]] 21:36, 13 December 2024 (UTC)
:"outside of the apocalypse" - we are talking about NYC :P [[Special:Contributions/172.69.64.171|172.69.64.171]] 00:04, 14 December 2024 (UTC)
:: With a Bostonian leading the discussion 👹 [[Special:Contributions/162.158.42.157|162.158.42.157]] 16:51, 14 December 2024 (UTC)
:The difference between the altimeter setting and the SLP is also pretty concerning. My understanding (which is based only on a few minutes of googling, not any actual experience) is that one does not correct for temperature while the other does, based on a 12 hour average. So maybe the high value is due to crazy temperatures? Haven't done any calculations, but it would fit the apocalyptic scenario. [[Special:Contributions/172.70.247.9|172.70.247.9]] 08:40, 14 December 2024 (UTC)
::That sounds about right for the weather station {{w|Belvedere Castle|located}} at the ZIP code [[1245: 10-Day Forecast|-10021]]... [[Special:Contributions/172.70.91.11|172.70.91.11]] 09:37, 14 December 2024 (UTC)

Damn, Randall says you got No Bitches.[[User:Xurkitree10|Xurkitree10]] ([[User talk:Xurkitree10|talk]]) 06:20, 14 December 2024 (UTC)

3015: D&D Combinatorics

2024-11-23T19:26:27Z

162.158.42.157: /* Explanation */

{{comic
| number = 3015
| date = November 22, 2024
| title = D&D Combinatorics
| image = dnd_combinatorics_2x.png
| imagesize = 328x446px
| noexpand = true
| titletext = Look, you can't complain about this after giving us so many scenarios involving N locked chests and M unlabeled keys.
}}

==Explanation==
{{incomplete|Created by a BOT THAT GRABBED A CURSED ARROW - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

Dungeons and Dragons (D&D) is a role-playing game that usually has a "Dungeon Master" (narrator) that takes a team of players through scenarios where they attack monsters and go on quests.

Often, there will be semi-random events: e.g., when attacking a monster, often a player will roll a die and deal damage based on the result. D&D uses a variety of dice, from regular d6 (6-sided, cubic dice) to other polyhedral dice, with the number of faces denoted by dX (e.g., d10 is a 10-sided die, with numbers from 1 to 10 on it). Common sets include: d4, d6, d8, d10, d12, d20, and occasionally d100 (typically not, however, the [[2626:_d65536|d65536]]).{{cn}}

With these, you can simulate events with a wide variety of denominators. In this case, Cueball gives a {{w|combinatorics|combinatorial}} problem:

* There are 10 arrows.
* 5 arrows are cursed.
* You randomly take two.
* What are the odds that neither of them are cursed?

Calculating using {{w|binomial coefficients}}, there are “10 choose 2” (45) ways to choose two arrows, of which there are “5 choose 2” (10) ways to choose 2 arrows that are non-cursed. As a result, the odds of taking all non-cursed arrows is 10/45, which simplifies to 2/9.

The Dungeon Master (DM) in this case [[356: Nerd Sniping|has to]] map that probability into rolling multiple dice, whose sums are also not evenly distributed: i.e. if rolling 3d6 (3 six-sided dice) and a d4 (1 four-sided die), the sums can range from 4 to 22. It's pretty hard to do this in one's head, but it does happen that the odds of rolling 16 or more with this combination is 2/9, matching the probability that we want to simulate. The caption elaborates that the DM has a degree in the relevant field, and is unable to resist applying this to the D&D game when the opportunity arises - opportunities that Cueball eagerly provides for this very reason.

There is a much easier way of implementing the operation: literally present 10 similar-looking arrows, or other objects that are taken to represent arrows (cards, for example), with the assigned information of whether each one is cursed hidden away from Cueball, and then let Cueball pick any two. It may be inferred that as the DM's mind is too occupied with advanced, high-level knowledge, she is no longer capable of considering straightforward solutions to the problem. Or that the DM actually enjoys calculating probabilities and combinatorics in a geeky way.

The title text claims that Randall only started doing this to the DM after she herself insisted on forcing another combinatorial puzzle on the players several times, involving a bunch of locked treasure chests and a multitude of keys to unlock them with. This might be a reference to an M-of-N encryption system, where a system has ''n'' valid passwords (instead of just one) but requires ''m'' of those passwords to be given before it will open; it is assumed m is greater than 1 but less than n. While this is easy enough to implement in a computer system, it would be extremely cumbersome to build for a physical lock with keys, and spreading the mechanism across multiple separate treasure chests would be impossible without literal magic (luckily, magic is in plentiful supply in a typical Dungeons and Dragons game).

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[Cueball, Megan, Ponytail, White Hat, and Knit Cap are sitting at a table. Everyone is looking at Cueball. Ponytail is facepalming. The table is covered in sheets of paper and assorted dice.] 
:Cueball: I grab 2 of the 10 arrows without looking and fire them, hoping I didn't grab one of the 5 cursed ones. Did I?
:Ponytail: Sigh. Umm. Okay.
:Ponytail: Roll... Uh... Hang on...
:Ponytail: Roll 3d6 and a d4. You need... 16 or better to avoid the cursed arrows.

:[Caption below the panel:]
:I got '''''way''''' more annoying to play D&D with once I learned that our DM has a combinatorics degree and can't resist puzzles.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring White Hat]]
[[Category:Comics featuring Knit Cap]]
[[Category:Games]]
[[Category:Math]]