Timeline for Correct way to add 22 to 4 to get given value
Current License: CC BY-SA 3.0
18 events
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| Feb 10, 2017 at 12:29 | comment | added | Jakob Pamp Bengtsson | @LaconicDroid I, family member and friends here in Sweden use it. I'd say it's fairly prevalent. We interchangeably use "Klockan 10" and "Klockan 22" ([o'clock] effectively), though we can use shorthand in conversation; "Vilken tid?" "Runt 22" (When? Around 22), and even if it is uncommon to not use o'clock or something similar for further specification, I don't see a real problem with omitting it for puzzling purposes. | |
| Feb 10, 2017 at 12:27 | comment | added | Laconic Droid | @JakobPampBengtsson You are free to disagree with the convention. But 22 is still not a time in the same way 22.344566 is not a time. If you have examples to cite where "22" is used as a time I'd be very surprised. | |
| Feb 10, 2017 at 9:35 | comment | added | Jakob Pamp Bengtsson | @LaconicDroid I disagree with your reasoning. If 22 is not a time, why is 22:00 a time? You're just specifying it more precisely. Why aren't you required to specify it as 22:00:00? And obviously the same argument would follow until we reach the smallest amount of measurable time, which would lead into a discussion about the concept of time. So I argue that 22 IS a valid time, just like, for example, January 3rd is. Now, if I continue this: If it's Jan 3rd and you add 366 days (not a leap year), what date is it? You typically wouldn't add "... and a year". 22 + 4 hours = 2 o'clock seems fine. | |
| May 28, 2016 at 14:23 | comment | added | Tom Carpenter |
There is nothing base-24 or base-12 about time. Otherwise right now it would be A:AAam (base-12) or A:M am (base-24), but we don't say that, we say it is 10:22 (base-10). Hours, minutes, seconds are all expressed in decimal. However they are calculated modulo (24 for hours, 60 for minutes and seconds). Modulo != base. So to do 22+4 in terms of hours, the calculation would be: $(22+4)\pmod{24}=2$ - so it is still addition.
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| May 28, 2016 at 10:37 | comment | added | Jamie Hanrahan | Also, 22:00 plus 4 hours does not produce 02:00. It yields 02:00 plus one day. The same objection applies to the "months" answer. See "words that end in GRY": xkcd.com/169 | |
| May 27, 2016 at 19:56 | comment | added | Laconic Droid | "22" is also not a time. The time would be 22:00. Same for "4" which would be represented as 04:00. So while I expect this is the correct answer, it's a terrible question. | |
| May 27, 2016 at 17:14 | comment | added | Jason |
@mstrz the numbers 22, 4 and 2 are expressed in decimal format but they are not being used in a decimal system. It would be more appropriate to call them the numbers m, 4 and 2 in a number system from 0-n in the same way hex is a number system from 0-f - in this case, m + 4 = 12 - so still not entirely straight forward.
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| May 27, 2016 at 17:09 | comment | added | Jason | @JeffreyKemp the fact that we express the 24 hours in a day in decimal format doesn't change the fact that a decimal unit is 1/10 and an hour is 1/24 (and a binary unit is 1/2, octal unit is 1/8, hex unit is 1/16...). | |
| May 27, 2016 at 11:17 | comment | added | mstrz | And I have to agree with Chris Burt Brown. The numbers 22, 4 and 2 are decimal (base-10) numbers in this question. Period.If they were tetravigesimal (base-24) then !22<sub>tv</sub> (50<sub>d</sub>) + 4<sub>tv</sub> (4<sub>d</sub>) = 26<sub>tv</sub> (54<sub>d</sub>) which equals 2 in neither of bases. @antipattern if you wrote hexadecimal F as 15 and said it was a hexadecimal number it would make it 15h = 21d. If you said it was dec. it would be OK. | |
| May 27, 2016 at 8:50 | comment | added | Yiorgos Moschovitis | two dozen hours in a day... | |
| May 27, 2016 at 6:11 | comment | added | Lamar Latrell | metric time... | |
| May 27, 2016 at 2:19 | comment | added | Jeffrey Kemp | Huh? If these numbers are "not decimal", how many hours are there in a 24-hour day? | |
| May 26, 2016 at 22:52 | comment | added | Yiorgos Moschovitis | I have to agree with @antipattern. Hours are not decimal. Hours are either duodecimal (12) or tetravigesimal (24). In this nonsense is using both to make an addition (!) but clearly not using decimal (10). | |
| May 26, 2016 at 12:12 | comment | added | Chris Burt-Brown | @antipattern: Just because the question is using modular arithmetic doesn't mean it is not base 10. The hour resets after 23 but you can express that in decimal or whatever base you like. | |
| May 26, 2016 at 12:09 | vote | accept | A J | ||
| May 26, 2016 at 12:04 | comment | added | antipattern | While this is most likely the right answer, the interviewer mislead by answering that "the numbers are decimal", which would mean they wrap around at 9+1. Which is very obviously not the case here. If I wrote hexadecimals as 0-15 that would still not make them decimal. | |
| May 26, 2016 at 10:57 | comment | added | Gareth McCaughan♦ | I think this is almost certainly the right answer (and just a bit better than the suggestion of months) but I remark that whenever a,b,c are integers with c<a+b you can answer "how do you add a to b and get c?" with "by doing the addition modulo a+b-c"... | |
| May 26, 2016 at 8:21 | history | answered | KoA | CC BY-SA 3.0 |