explain xkcd - User contributions [en]

2379: Probability Comparisons

2020-10-31T05:00:01Z

FlyingPiMonster: /* Explanation */ Add title text explanation

{{comic
| number = 2379
| date = October 30, 2020
| title = Probability Comparisons
| image = probability_comparisons.png
| titletext = Call me, MAYBE.
}}

==Explanation==
{{incomplete|Created by LEBRON JAMES THROWING BASKETBALLS AT A KEYBOARD. The table for the explanations of the chances isn't complete. Do NOT delete this tag too soon.}}

This is a list of probabilities for different events. Recurring themes include M&Ms, Scrabble, polyhedral dice, a white Christmas and basketball.

The probabilities are calculated from [https://xkcd.com/2379/sources/ these sources], as mentioned in the bottom left corner.

{| class="wikitable sortable"
! Odds
! Text
! Explanation
|-
| 0.01%
| You guess the last four digits of someone's {{w|Social Security Number}} on the first try
|(1/10)4 = 0.0001, or 0.01%
|-
| 0.1%
| Three randomly chosen people are all left-handed
| The chances of being left handed is about 10%, and 10%3 = 0.1%.
|-
| 0.2%
| You draw 2 random {{w|Scrabble}} tiles and get M and M You draw 3 random {{w|M&Ms}} and they're all red
|
|-
| 0.3%
| You guess someone's birthday in one try.
| Matching birthdays is more likely than might be expected; see {{w|Birthday problem}} for details.
|-
|}

The title text refers to the song [https://en.wikipedia.org/wiki/Call_Me_Maybe Call Me Maybe] by Carly Rae Jepsen. "MAYBE" is emphasized because the probability of getting her phone number correct, as in the last item in the list, is very low.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

{{comic discussion}}
[[Category:Statistics]]
[[Category:Comics featuring real people]]

2089: Christmas Eve Eve

2018-12-25T03:25:02Z

FlyingPiMonster: Add to Christmas category

{{comic
| number = 2089
| date = December 24, 2018
| title = Christmas Eve Eve
| image = christmas_eve_eve.png
| titletext = It turns out that saying "Oh, so THAT'S why they call it Boxing Day" is a good way to get punched a second time.
}}

==Explanation==
{{incomplete|Created by SANTA. There appears to be no explanation. Do NOT delete this tag too soon.}}

This comic was posted on December 24, 2018.

The evening or day preceding a special day such as a holiday is often referred to as the ''eve'' of that day (derived from the same word from which we get ''evening''). Thus December 24 is Christmas Eve.
Some people extend this and call December 23 "Christmas Eve Eve." The day before ''that'' would be "Christmas Eve Eve Eve," adding one "Eve" for each night before Christmas morning.

Cueball notes the general idea, and Megan acknowledges it. Cueball follows by naming December 24 as Christmas Eve, December 25 as Christmas, and then mentions that the following day is his favorite.
Megan's "Oh no" implies that she knows what Cueball will say next.

Since December 26 is the 364th day before Christmas (when the following year is not a leap year), it follows that it is "Christmas" followed by "Eve" 364 times.

Megan finds listening to Cueball recite this unacceptable; as such, she announces that she will not give him gifts, taking the extra step of returning the gifts she'd already bought.

The title text refers to the [[wikipedia:Boxing Day|Boxing Day]] holiday celebrated the day after Christmas in the UK and many parts of the former British Empire. Although the name officially refers to servants boxing up the presents they get from their masters, most Americans don't know this and make jokes about how it refers to {{w|Boxing|the sport of boxing}}. In this title text we can presume Cueball was punched (or ''boxed'') after his litany of 364 ''Eve''s, to which he replies, "Oh, so that's why they call it Boxing Day," only to be punched again.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon. I demand a recount!}}

[Cueball, White Hat, and Megan stand in frame.]

Cueball: Today is Christmas Eve. Yesterday was Christmas Eve Eve.

Megan: Uh huh...

Cuball: Of course, tomorrow is Christmas. And then, my favorite...

Megan: Oh no.

Cueball: ...Christmas Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve!

[The ''Eve''s get smaller from line to line.]

Megan: I'm returning the presents I got you.

{{comic discussion}}
[[Category:Christmas]]

2073: Kilogram

2018-11-16T16:16:34Z

FlyingPiMonster: Change "International Bureau of Weights and Measures" to "International Committee for Weights and Measures"

{{comic
| number = 2073
| date = November 16, 2018
| title = Kilogram
| image = kilogram.png
| titletext = I'm glad to hear they're finally redefining the meter to be exactly three feet.
}}

==Explanation==
{{incomplete|Created by a BOT. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}
The day of this comic, the International Committee for Weights and Measures voted to redefine the kilogram by fixing the value of Planck's Constant. The change will take effect on May 20, 2019, when the platinum cylinder International Prototype Kilogram that defines the unit will be retired. This means that the mass of a kilogram will no longer be tied to a physical object, but to the fundamental properties of the universe.

In this comic, Black Hat announces that the kilogram has been redefined as equal to one pound. Ponytail and Cueball seem to think this makes things simpler, but Megan is rightfully alarmed. The metric system of measurement is the one used by most of the world and is the standard system used in science. It is considered superior to the imperial system (which the pound is part of). Therefore, redefining the kilogram to be based on the pound would make things much, much worse and outrage supporters of the metric system.

To add to the confusion, the pound is officially defined as 0.45359237 kilograms. This makes defining a kilogram as one pound is impossible.

The title text continues the joke by saying that the meter has been defined as exactly three feet. The yard, the closest imperial measurement to the meter, is three feet. However, a meter is about 9 centimeters longer than a yard.

==Transcript==
:[Black Hat talking to Ponytail, Cueball, and Megan while all stand in a row. Megan's hands are raised emphatically.]
:(From top left to bottom right)
:Black Hat: To end many years of confusion, the international committee for weights and measures has just voted to redefine the kilogram.
:Black Hat: As of next May, it will equal exactly one pound.
:Ponytail: Oh, cool.
:Cueball: That does make things simpler.
:Megan: No!!
{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Black Hat]]
[[Category:Comics featuring Ponytail]]
[[Category:Physics]]

2073: Kilogram

2018-11-16T16:14:50Z

FlyingPiMonster: Explain the comic in light of the recent (real) redefinition of the kilogram

{{comic
| number = 2073
| date = November 16, 2018
| title = Kilogram
| image = kilogram.png
| titletext = I'm glad to hear they're finally redefining the meter to be exactly three feet.
}}

==Explanation==
{{incomplete|Created by a BOT. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}
The day of this comic, the International Bureau of Weights and Measures voted to redefine the kilogram by fixing the value of Planck's Constant. The change will take effect on May 20, 2019, when the platinum cylinder International Prototype Kilogram that defines the unit will be retired. This means that the mass of a kilogram will no longer be tied to a physical object, but to the fundamental properties of the universe.

In this comic, Black Hat announces that the kilogram has been redefined as equal to one pound. Ponytail and Cueball seem to think this makes things simpler, but Megan is rightfully alarmed. The metric system of measurement is the one used by most of the world and is the standard system used in science. It is considered superior to the imperial system (which the pound is part of). Therefore, redefining the kilogram to be based on the pound would make things much, much worse and outrage supporters of the metric system.

To add to the confusion, the pound is officially defined as 0.45359237 kilograms. This makes defining a kilogram as one pound is impossible.

The title text continues the joke by saying that the meter has been defined as exactly three feet. The yard, the closest imperial measurement to the meter, is three feet. However, a meter is about 9 centimeters longer than a yard.

==Transcript==
:[Black Hat talking to Ponytail, Cueball, and Megan while all stand in a row. Megan's hands are raised emphatically.]
:(From top left to bottom right)
:Black Hat: To end many years of confusion, the international committee for weights and measures has just voted to redefine the kilogram.
:Black Hat: As of next May, it will equal exactly one pound.
:Ponytail: Oh, cool.
:Cueball: That does make things simpler.
:Megan: No!!
{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Black Hat]]
[[Category:Comics featuring Ponytail]]
[[Category:Physics]]

1935: 2018

2018-01-01T05:14:40Z

FlyingPiMonster: Change the trivia about the last comic of 2017 to past tense

{{comic
| number = 1935
| date = December 29, 2017
| title = 2018
| image = 2018.png
| titletext = We should really start calculating it earlier, but until the end of December we're always too busy trying to figure out which day Christmas will fall on.
}}

==Explanation==

In this [[:Category:New Year|New Year comic]], [[Megan]] wonders if 2018 will be a {{w|Leap year|leap year}}. [[Cueball]] thinks 2018 will not be a leap year, and Megan responds that she "doubts anyone knows at this point." This appears to be a jab at the complexity of the leap year system. As Cueball says, leap years occur every four years (though there are a few exceptions), adding an extra day to account for the fact that Earth takes a bit longer than 365 days to orbit the Sun. Therefore, most years that are a multiple of four are leap years. As Megan says, this is easy for odd-numbered years, since no odd numbers are divisible by four. However, for even-numbered years, it isn't always obvious.

The last panel expresses a misunderstanding of modern public-key {{w|Cryptography|cryptography}}, which relies on the fact that it is difficult to factorize large numbers. Megan is applying this concept to the year, claiming that it is hard to determine whether or not 2018 is a multiple of four and hence is a leap year. In reality, factorization is not needed here, since we already know the factor, which is four. Megan states that if it were possible to factor large numbers with a calculator, modern cryptography would collapse. While true, it is only true for truly large numbers (hundreds of digits), and no factorization is needed in this case.

At the end of the strip, Megan hopes the answer can be {{w|Brute-force attack|brute-forced}} by February. Brute force is a method of breaking cryptography by trying every possible option until one works. This is a misdirection upon misdirection, in that even if we needed to factorize 2018 (which we don't), the simplest brute forcing algorithm would only need to try 43 numbers - from 2 to square root of 2018 (44). In cryptography, the algorithms use numbers much, much bigger than 2018 -- on the order of hundreds (or even thousands) of digits.

The title text refers to calculating which day {{w|Christmas}} will fall on. Given that it always falls on December 25th (in western countries), there is nothing to calculate. They could mean which day of the week, so it's either the 359th or the 360th (leap years) day of the year and the day of the week may differ. This is a reference to Easter whose date jumps from year to year according to a complicated algorithm that most people don't know. The changing date of Easter was recently included in [[1930: Calendar Facts]].

==Transcript==

:[Megan is walking.]
:Megan: I wonder if 2018 will be a leap year.

:[Now it turns out that Cueball walks behind Megan.]
:Cueball: ...it won't be, right?
:Megan: I doubt anyone knows at this point.

:[Same scene in a frame-less panel.]
:Cueball: No, it's definitely not. Leap years are divisible by 4.
:Megan: Right, and for odd numbers, that's easy.
:Megan: But 2018 is even.
:Megan: 50/50 chance.

:[Zoomed-out view with both walking in silhouette on a dark slightly curved ground.]
:Cueball: I can settle this with a calculator.
:Megan: No way. If it were easy to factor large numbers like that, modern cryptography would collapse.
:Cueball: I see.
:Megan: I just hope we manage to brute-force it by February.

==Trivia==
*Released on Friday, December 29, this was the last comic of 2017. The next comic, [[1936: Desert Golfing]], was released soon after midnight (in Randall's time zone) on New Year's Day 2018.

*Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100, but these centurial years are leap years if they are exactly divisible by 400. For example, the years 1700, 1800, and 1900 were not leap years, but the years 1600 and 2000 were.

*Since 100 is divisible by 4, only the last two digits of a number are needed to determine if that number is divisible by 4. So to determine if 2018 is divisible by 4, we only need to check whether 18 is divisible by 4, which is easy.

*2018 is not divisible by 4, so the year is not a leap year. 2016 and 2020 are leap years. Assuming your calendar is Gregorian! A year is roughly 365.2422 days long. (Actually, also the case if it is 2018 on the old Julian calendar. The century year rules for leap years are different on the Gregorian calendar from the Julian, but the non-century year rules are the same).

*{{w|Eastern Christian Churches}} celebrate Christmas also on December 25 but of the older Julian calendar, which currently corresponds to January 7 in the Gregorian calendar.

*This is the third year in a row with New Year's comics with only the year used as the title, before that there were two more comics with such titles, but those two (and thus the first three) were only released in the even years: [[998: 2012]] in 2012, [[1311: 2014]] in 2014, [[1624: 2016]] in 2016 and [[1779: 2017]] in 2017.

{{comic discussion}}

[[Category:New Year]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Cueball]]
[[Category:Comics sharing name|2017]]
[[Category:Math]]
[[Category:Time]]
[[Category:Cryptography]]

Talk:1935: 2018

2017-12-29T18:08:22Z

FlyingPiMonster: /* Title text explanation mis-read */

This is easy! Don't factor it - just multiply by 25 and if that ends in two zeros, but not four zeros then it's a leap year, at least most of the time.....17:25, 29 December 2017 (UTC)

This is easy! Don’t factor it - just convert it into a binary and look at the 2 least significant bits. If they are 00 the number is multiple of four. —[[Special:Contributions/172.69.33.35|172.69.33.35]] 17:37, 29 December 2017 (UTC)

This is easy! Don't factor it - just subtract 4 repeatedly. If you end up at 0, it's divisible. If you end up at 1, 2, or 3, it's not. -- 17:55, 29 December 2017 (UTC)

== Title text explanation mis-read ==

Explanation of title text is incorrect:

"The title text refers to calculating the date of Christmas; again, this is a trivial exercise, because Christmas is always December 25."

Title text states 'day of Christmas', not 'date...'. The day changes each year and so does require calculation.

Oops, my bad. Fixed. [[User:FlyingPiMonster|FlyingPiMonster]] ([[User talk:FlyingPiMonster|talk]]) 18:08, 29 December 2017 (UTC)

1935: 2018

2017-12-29T18:07:49Z

FlyingPiMonster: Fixed explanation of title text

1935: 2018

2017-12-29T17:47:16Z

FlyingPiMonster: Added an explanation

1833: Code Quality 3

2017-05-05T13:58:10Z

FlyingPiMonster: Add explanation

{{comic
| number = 1833
| date = May 5, 2017
| title = Code Quality 3
| image = code_quality_3.png
| titletext = It's like a half-solved cryptogram where the solution is a piece of FORTH code written by someone who doesn't know FORTH.
}}

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

This comic is a direct continuation of [[1513: Code Quality]] and [[1695: Code Quality 2]] in the [[:Category:Code Quality|Code Quality]] series, in which Ponytail continually insults Cueball's code style. In this comic, as in the previous, Cueball does not directly appear, only speaking off-panel; however, as it is a continuation of the series, it is clear that this is Cueball's code.

In the first panel, Ponytail references [https://en.wikipedia.org/wiki/Query_string query strings], which store information, such as search queries or page numbers, relevant to the URL. Query strings are not meant to be especially human-readable, so a song based on one would likely not be a good one.

A tactical light is a light that can be mounted on a gun for use in low-light scenarios. They tend to be very durable and very bright. Different models have different features and capabilities, so they are given cool-sounding model numbers. A JSON table of these model numbers would look like random data.

[https://en.wikipedia.org/wiki/Alan_Turing Alan Turing] was a British theoretical computer scientist, often considered the father of the field. His 1936 paper outlined Turing machines, a theoretical model for computing, as well as computability and the halting problem. Theoretical computer science is very different from practical coding; understanding the contents of the paper would not at all help a coder to understand today's algorithms, design patterns, and best practices.

In the final panel, Ponytail references [https://en.wikipedia.org/wiki/Leet leet-speak], in which symbols are replaced with similar-looking symbols, and a [https://en.wikipedia.org/wiki/Manifesto manifesto], a statement of a person or group's beliefs and intentions. A manifesto from a survivalist cult leader would likely be nonsensical, even before being translated to leet-speak. Memory allocation is a low-level computer programming concept; most modern languages have features that take care of memory allocation for the programmer, possibly implying that Cueball does not know how to use these features.

At the end of the final panel, Cueball, seeing that Ponytail is tired of reading his code, offers to ask someone else to read his code. Ponytail insults him again by saying that nobody would want to review his code after seeing it for the first time.

[https://en.wikipedia.org/wiki/Forth_(programming_language)#Programmer.27s_perspective Forth] is an old programming language that tends to be difficult to read. A [https://en.wikipedia.org/wiki/Cryptogram cryptogram] is a cipher puzzle, generally one easy enough to be solved manually. The title text implies that the code is so bad that it looks like unreadable FORTH code that is missing random characters.

==Transcript==
:[Ponytail sitting in front of a computer screen typing. Cueball speaks only off-panel, but since this is a direct continuation of comic 1513 and 1695: Code Quality and Code Quality 2 where Cueball is shown, there can be no doubt it is him.]
:Ponytail: Your code looks like song lyrics written using only the stuff that comes after the question mark in a URL.
:Cueball (off-panel): Sorry.
:[Zoom in on Ponytail.]
:Ponytail: It's like a JSON table of model numbers for flashlights with "tactical" in their names
:[Zoom back out again]
:Ponytail: Like you read Turing's 1936 paper on computing and a page of JavaScript example code and guessed at everything in between.
:[Zoom in again on Ponytail's face]
:Ponytail: It's like a leet-speak translation of a manifesto by a survivalist cult leader who's for some reason obsessed with memory allocation.
:Cueball (off-panel): I can get someone else to review my code
:Ponytail: Not more than once, I bet.

{{comic discussion}}

[[Category:Code Quality]]