Randall is introducing the rules of the game Expiration Date High Score hence the title.
If you find an item which you purchased, but is now past its expiration date, you get a score which is what percent of your lifetime elapsed between when the item expired and when you found it.
Megan, looking in a cupboard, find a can of beans that expired in 2010 (9 years ago), and that gives her a score of 24.3. Megan's age is thus revealed to be 37, found by substituting 2019 and 2010 into the formula 100*(2019-2010)/<age> = 24.3 and solving for the age.
Cueball then remarks that she will never beat her mom's jar of pickles that was from 1978. Megan then wonders if there are more cans (from 2010 or before) in the cupboard, and asks Cueball to remind her to not look any further until 2030. At that time the can would have been 20 years old and she would be 48, giving such a can a score of 100*(2030-2010)/48 = 41.6. That would thus beat her mom's high score.
If her mom's jar had expired in 1978 (not clear from the text), and for instance was found last year in 2018, then the formula for the mother's score would be 100*(2018-1978)/<Mom's age>. And this should then not be more than 41, thus revealing the mother age to be around 100 years old today (98 last year). Of course the jar could have had an expiration day some years later, or have been found earlier. Otherwise Megan's mom would have been above 60 when giving birth to Megan. Of course Megan could also just take this extra long wait in case the next can is not from 2010 but only 2013 etc.
Cueball's final remark is that this is a terrible competition, the worst ever. Because keeping food that can spoil could potentially be dangerous, if not so, at least disgusting when finally trying to get rid of it later.
Many perishable items, such as food, cosmetics, medications, batteries, or condoms, have expiration dates, or sometimes best by dates. The only other rule is, that it has to be something you have purchased yourself, so that heritages or stuff that was left in the basement when one moved in, does not count. A score of 100 or higher would indicate the item expired when you were born or before you were born, meaning it was already expired when you purchased it.
The joke is, that owning expired items without noticing for a long time, is here getting you a high score, while in reality it is not considered favorable to have food that has expired long time ago.
The other joke is both the items in the comic (a can of beans and a jar of pickles) do not go bad with time but in fact remain edible indefinitely (as long as the jar/can is not opened and is undamaged.) 
Food going bad, in the sense that it will make you sick if you eat it, is most often caused by harmful bacteria growing in the food. Less often caused by fungi or yeast growing in the food and creating a poisonous substance, like methanol (wood alcohol.) The process of canning food involves boiling it to kill all possible pathogens, then sealing it in a can/jar while the food is still hot, with no air bubble. As long as this process is done correctly, as long as the jar lid has an air tight seal, and as long at the can is not punctured or gets a hole rusted through, no bacteria/virus/yeast/fungi can get in and the food cannot spoil. Some food may discolor over time in the jar/can, or the texture may change, but it cannot go bad in a way that makes it unsafe to eat.
Megan's mom could not have a jar of pickles with a 1978 expiration date because in 1978 jars and cans of food did not have expiration dates. Since then many countries introduced laws and regulations requiring companies to put expiration dates on perishable goods. In some instances this can have the negative effect of people throwing out good food by blindly following the suggested expiration date. This behavior can incentivize companies to adjust the expiration date, or put expiration dates on non-perishable goods, so that people will re-buy the products sooner.
The title text continues the conversation from the comic. Cueball remarks that they moved since 2010... Thus the beans were apparently bought while living in a different home, meaning they were moved along with their other belongings. This is somewhat unusual as many people take moving as an opportunity to go through their old stuff and get rid of things they no longer need. Since the rules clearly states that you have to have bought it yourself, it could not have been in the house when they moved in, they had to have brought it along (unless they later bought something that was already expired). But given Megan's final answer that "some of us were just born to be champions" indicates that she did bring it along, anticipating this game, and thus given her self a great score. And as is clear she is willing to wait 11 years to try to beat her mom's score.
It is not clear why they are keeping items for long periods of time in order to win. An easier way to win this game would be to buy food that is already expired. One could obtain a score of 100 simply by buying something that expired when one was born, and finding it the next day.
- [Title up in the panel:]
- What's the most expired item you've found in your house?
- Calculate your
- Expiration Date High Score
- (must be something you purchased)
- [Equation in a circle:]
- Score = (year you found item) minus (year item expired) divided by (your age when you found it), multiplied by 100
- [Megan and Cueball talking in a kitchen, with Megan holding a can.]
- Megan: These beans expired in 2010! That's... let's see... 24.3! New personal best!
- Cueball: You're never going to beat your mom's jar of pickles from 1978.
- Megan: Maybe there are more cans in there. Remind me not to look until 2030.
- Cueball: This is the worst competition.
The formula suggests Megans age to be 37, if this comic plays in 2019, when it was released. That puts her birth year to either 1982 or 1981 (depending on whether this plays before or after her birthday in 2019). This is in slight contrast to 630: Time Travel, which implies her birth year to be 1983.
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If we assume this comic is contemporary, i.e. the year she found the beans is 2019, it makes Randall's girlfriend/wife 37 years old.188.8.131.52 05:25, 19 July 2019 (UTC)
- Well... it makes Megan 37 years old. There is nothing here to strongly suggest that cueball and her are Randall and his gf/wife. --Lupo (talk) 05:54, 19 July 2019 (UTC)
- Well, to be exact it makes Megan 37 years, 13 days, 12 hours, 7 minutes, 13.3 seconds old (rounded to the nearest tenth of a second). This is based on 900/24.3 = 37.0370 (...) That would make her born on July 6, 1982 (if we work back from the date of publication of the comic). But to be realistic I guess she was probably rounding the score to the nearest decimal, rather than writing 24.32432... (i.e. 900/37), in which case I'm wrong. Either way, spurious accuracy is fun!! 184.108.40.206 19:07, 20 July 2019 (UTC)
What about #933? 220.127.116.11 21:35, 19 July 2019 (UTC)
- I think it's pretty clear that the title text varies from comic to comic. Sometimes it's clearly a character's voice. Sometimes it makes more sense as a narrator's voice. Sometimes it's clearly talking about Randall's life. I realize that this site tends to attribute the title text to Randall's voice, but personally, I consider it an unattributed voice. Sometimes it's him, sometimes it's more of a narrator or character voice. Similarly, the actions in the comics are sometimes clearly influenced by events in Randall's life, but they're also clearly not other times. If it turned out that he made Megan 37 because his wife is 37, that wouldn't surprise me, but neither would it surprise me if he did something different, because he does that on a regular basis. (In other words, without additional evidence or supporting information, I think it's weird to state as a fact that the traits of various characters are, in fact, traits of Randall and his friends and family.) Mootstrap (talk) 02:38, 20 July 2019 (UTC)
- Yes. I'm not RM but if I were I'd just write in a pretty number that has no meaning at all just to be done with the comic. 18.104.22.168 03:58, 20 July 2019 (UTC)
When I was working at a gas station, someone brought in a propane tank which had expired in 1963 (or so). If 1963 and using this scheme, my score would be 96.6.
22.214.171.124 06:02, 19 July 2019 (UTC)
- Did you buy the propane tank, though? --126.96.36.199 07:09, 22 July 2019 (UTC)
Propane tanks do not "expire", that is they do not go bad with time, and you do not need to throw them out after the date. The date on these tanks is when they need to be inspected for damage, as mandated by Federal and state laws. If the tank passes inspection a new date in put on and you can keep using the tank (propane suppliers can legally keep refilling it.) Godzilla (talk) 13:40, 19 July 2019 (UTC)
- Except that it
must be something you purchased so you can't use that one in the contest. Unless you then purchased it from whoever brought it in…
I don't see any rule requiring that the item be new (or otherwise not-yet-expired) when you purchase it, so can we buy old things from other people in order to inflate our score (potentially over 100)? 188.8.131.52 06:18, 19 July 2019 (UTC)
- That also circumvents the argument "we moved since 2010". If you buy the apartment with kitchen and all equipment, you also purchased the expired item... --Lupo (talk) 06:20, 19 July 2019 (UTC)
- I think that part in the title text is referring to "how did we manage to not come across all of our expired items when we moved" rather than "this item was here before me moved in". Some very disorganised people might actually pack up and move all of the items (e.g. food) in their house without first checking or even noticing if it is expired. 184.108.40.206 10:52, 19 July 2019 (UTC)
- That was my initial thought too, that she either did it without of noticing, or did not notice it on purpose, to at some point reach this score. But the loophole, good 'ol 42.76 brought up, put this idea up, as an alternative.--Lupo (talk) 10:56, 19 July 2019 (UTC)
- The rules say that the item must be something you, personally purchased...so did they BUY the pickles from Megan's mom? I'd want to see a receipt or something! (And if the pickles were dated to 1978, Megan (whom we've established is 37 years old was not born when the pickles were dated...so for sure, this is cheating! SteveBaker (talk) 13:36, 19 July 2019 (UTC)
- They clearly attribute the pickle score to Megan's mum, not to Megan.Bischoff (talk) 13:42, 19 July 2019 (UTC)
- Yeah - that makes more sense. I had initially read it as these were pickles MADE by her mum and given to Megan - not pickles that her mum purchased. Sadly, we can't work backwards from the 2030 date that Megan needs to wait until in order to beat that score to figure out her mom's age because we don't know on what year her mum discovered the ancient pickles. SteveBaker (talk) 13:48, 19 July 2019 (UTC)
There is one caveat to Megan's strategy: since the fraction (year you found item - year item expired)/(your age when you found it) converges to one as time goes on regardless whether the numerator is bigger than the denominator, as long as the item expired before the year of your birth, postponing the discovery reduces your score (considerably).
Her mom's pickles could still have had an expiration date before 1978 - according to this article they were around in the 1950s and on store shelves by 1970. If they were home-canned she could also have dated them herself. --220.127.116.11 17:56, 19 July 2019 (UTC)
- Perishable foods had expiration dates in the 1970s at least (maybe earlier in some countries and some stores). But non-perishable foods did NOT had dates until the 2000's or later. A home canned jar of pickles could have a hand written date, but this would be the date it was canned, not an expiration date. Because anyone in the 1970s who knew how to can would know if they did it right the food would not go bad. If they did the canning wrong they would not need a expiration date to know this, they would know in a few weeks, by looking through the mason jar at the food inside. Or by looking at the food and glass spread around the pantry after the jar exploded. So Megan's mom could have a loaf of bread with a 1978 date, but not a jar of pickles. Godzilla (talk) 18:17, 19 July 2019 (UTC)
I hereby fervently protest against the age-discriminating rules. 18.104.22.168 09:25, 22 July 2019 (UTC)
- Hear, hear! A 1-year-expired item shouldn't count 10 times more for a 10-year-old as for a 100-year-old.22.214.171.124 17:55, 22 July 2019 (UTC)
"Since then many countries introduced laws and regulations requiring companies to put expiration dates on perishable goods. In some instances this can have the negative effect of people throwing out good food by blindly following the suggested expiration date. This behaviour can incentivise companies to adjust the expiration date so that people will re-buy the products sooner."
Since science and the truth are a big part of both xkcd.com and explainxkcd.com, I think it is important this explanation includes how/why food goes bad, and why expiration dates on jars/cans of food do not serve to protect people from eating bad food. If no one else gets to it first I'll try to type this explanation when I get a chance.
Until then I don't think the explanation should say "...many countries introduced laws and regulations requiring companies to put expiration dates on perishable goods." Although this is true, it is also true many companies put expiration on non-perishable products even through there is no law requiring them to do so. Like cosmetics and jars of pickles. Godzilla (talk) 13:54, 19 July 2019 (UTC)
- To be fair, many items are labelled "Best Before" or "Sell By" - implying that the food item will be edible for at least some time beyond that date. Actual expiration dates on preserved food items do seem to be rarer. There are cases of canned food items from the early 1900's still being in good shape after 100+ years - and those would not have had any expiration date. But one issue is that back then, cans were made by soldering sheets of tin together - and the lead in the solder slowly leaches into the food making it unsafe to eat even though the food itself seems well-preserved. So for potential high scores, we should look to: The 11 oldest foods and beverages ever discovered - except that they'd not have any kind of formal expiration date. SteveBaker (talk) 14:10, 19 July 2019 (UTC)
- "it is also true many companies put expiration on non-perishable products" <- I especially like the "best before" date on salt. Bonus points if the box has a description of how the salt has been in a mine for over millions of years... --126.96.36.199 07:13, 22 July 2019 (UTC)
- To be fair, while the salt wouldn't go "bad" or spoiled, it WILL probably return to natural rock form, meaning will stop being loose. -- Hkmaly (talk) 23:22, 25 July 2019 (UTC)
- The legal requirements of "expiration dates" for food are less stringent than many believe. In the USA, under FDA regulations, only baby formula cannot legally be sold after its expiration date. Wording like "use by" and "sell by" is not legally binding... more like "guidelines", as Capt. Barbossa would say. 188.8.131.52 15:57, 19 July 2019 (UTC)
- Other than dairy, there are NO expiration dates, only the date the manufacturer wants to stop selling the product, for quality/taste/color/etc. SDSpivey (talk) 23:25, 22 July 2019 (UTC)
I think the point that needs to be made in the explanation is both the items in the comic (a can of beans and a jar of pickles) do not go bad with time but in fact remain edible indefinitely.
Food going bad, in the sense that it will make you sick if you eat it, is most often caused by harmful bacteria growing in the food. Less often caused by fungi or yeast growing in the food and creating a poisonous substance, like methanol (wood alcohol.) The process of canning food involves boiling it to kill all possible pathogens, then sealing it in a can/jar while the food is still hot, with no air bubble. As long as this process is done correctly, as long as the jar lid has an air tight seal, and as long at the can is not punctured or gets a hole rusted through, no bacteria/virus/yeast/fungi can get in and the food can not spoil. Some food may discolor over time in the jar/can, or the texture may change, but it can not go bad in a way that makes it unsafe to eat.
If the canning process is done incorrectly and bacteria/fungi/yeast is sealed in the can/jar, the food goes bad in a few weeks, not years. Gases given off by the decomposition process often cause the can to swell, or the normal concave jar lid to bulge upwards. Sometimes the internal gas pressure is enough to burst the can/jar, as used to happen to people who canned at home using mason jars. If it does not burst, you are still going the know the food has gone bad the minute you open the can/jar, even without looking inside.
The above facts are more important then who/how/why expiration dates get put on which products. Godzilla (talk) 17:13, 19 July 2019 (UTC)
SO my mom's fridge! When I was a kid, my brother had a buddy who would put on his best game show announcer voice and say "It's time for Search... For... Fungus!", then check the fridge for OLD things. Hysterical, laughed our heads off, and helped us out by getting rid of the old stuff, LOL! Me and her recently cleaned her fridge, and similarly found some pre-move items. LOL! NiceGuy1 (talk) 06:53, 20 July 2019 (UTC)
All Aussies can win this game with their personal vegemite jar. And they're still EATING it. 184.108.40.206 09:35, 20 July 2019 (UTC)
Canned food is first put into the can and sealed and then heated up to around 60~80 degrees Celsius. After it cools down, the label is placed on it. - sirKitKat
220.127.116.11 06:06, 21 July 2019 (UTC)
So, cool story, if the food is older than you are, your score will decline as you age. If you're older than the food, your score will increase ~ logarithmically.
If the food is older than you, you are still living with your parents, so it isn't your house, and your score doesn't count ;)
18.104.22.168 20:06, 22 July 2019 (UTC)
My mother has some of the same herbs in little tins that she had since shortly after she bought that house, in early 1969. Not doing the math, since she's not me. But it's probably a high score — Kazvorpal (talk) 01:42, 2 August 2019 (UTC)