Wikipedia:Reference desk/Archives/Miscellaneous/2017 January 13

= January 13 =

automotive water pump
My Chevy Cobalt has no aparent pulley for the drive belt (serpetine belt). If the drive belt is not powering the water pump then what is powering the water pump? 64.170.21.194 (talk) 01:18, 13 January 2017 (UTC)
 * I'm not sure, but it could be powered by gears, a clutch (such as a centrifugal or a magnetic clutch) or (on newer cars only) a self-contained electric motor. 2601:646:8E01:7E0B:3D95:7849:7362:98 (talk) 03:39, 13 January 2017 (UTC)


 * The chevy cobalt is a 2005 model. While some might not consider that a "newer car" It does have electric power steering instead of hydraulic power steering which people generally say "is a newer car thing". I wonder if an electric motor is used. I scoured through alldata and forums but I could not find any info on what actually powers the water pump. Thanks for the info ipv6. 64.170.21.194 (talk) 04:31, 13 January 2017 (UTC)


 * It is driven by the timing chain. http://www.autozone.com/cooling-heating-and-climate-control/water-pump/chevrolet/cobalt?vehicleSet=true 196.213.35.146 (talk) 06:13, 13 January 2017 (UTC)

The average cost for a Chevrolet Cobalt Water Pump Replacement in the US is between $606 and $890. Labor costs are estimated between $475 and $600 while parts are priced between $131 and $290. This estimate does not include taxes and fees. The link gives advice on the replacement procedure. Our article Chevrolet Cobalt mentions the fatality rates and recalls of this car model. Blooteuth (talk) 13:27, 13 January 2017 (UTC)

Passenger name records
Every time I take a flight, the booking has a unique passenger name record consisting of six characters. These could be either numbers or letters. It surprises me that there are apparently enough permutations of these six characters to be able to handle such a system. There must be hundreds if not thousands of flights taken every day, so I would have thought the possible PNR codes would run out fairly quickly. So how does the PNR numbering system actually work? And how many possible permutations are there of the six characters, being either numbers from 0 to 9 or letters from A to Z, assuming any of the characters can be repeated up to six times? Viennese Waltz 16:40, 13 January 2017 (UTC)
 * See permutations: The answer is 36!/(36-6)! which is 1,402,410,240 possible permutations. That's MORE than enough to give every person on earth a unique identifier.  1.4 trillion is 500 or so times the population of the earth.  -- Jayron 32 16:46, 13 January 2017 (UTC)
 * 1.4 billion, right? ←Baseball Bugs What's up, Doc? carrots→ 17:24, 13 January 2017 (UTC)
 * Yeah, I'm an idiot. Ignore me.  -- Jayron 32 17:25, 13 January 2017 (UTC)
 * What happens when the 1,402,410,241st human books air travel? Sagittarian Milky Way (talk) 17:59, 13 January 2017 (UTC)
 * By that time, we'll all have flying cars or teleportation booths. Clarityfiend (talk) 01:15, 14 January 2017 (UTC)
 * Wouldn't the calculation be 36 to the 6th power? Though that still only allows for something over 2 billion. ←Baseball Bugs What's up, Doc? carrots→ 18:12, 13 January 2017 (UTC)
 * Yes, the number of possible 6 letter words from a 36 letter alphabet is 366. I don't know how User:Jayron32 got his result.  According to our Record locator article, 5 characters are not used (1, I, L, O, and 0), so the actual number of record locator codes is 316 = 887.503,681.  According to our article, codes can be reused after "the data to which it refers has been purged from the system", whatever that means, but it seems that the codes don't need to be unique for all time.  CodeTalker (talk) 20:00, 13 January 2017 (UTC)


 * Looks like you put a period in that number, where a comma belongs. StuRat (talk) 17:49, 15 January 2017 (UTC)


 * Also, from looking at the article, it looks like there isn't one globally unique set of PNRs. They're only unique within a given registration system. In other words, it's the same as any arbitrary ID number a given organization, like a bank or utility, might assign to you; it has no particular relevance outside of their own systems. --47.138.163.230 (talk) 20:16, 14 January 2017 (UTC)


 * "I don't know how User:Jayron32 got his result." They were probably thrown off by the OP's use of the word "permutations", which implies no reuse of the same symbol in an individual code.
 * Math vocabulary question: Permutation refers to picking without replacement while retaining order, so that nPk = n!/(n-k)!. Combination refers to picking without replacement without retaining order, so that nCk = n!/[(n-k)!k!].  What term is used for picking with replacement while retaining order, so that n?k = nk?  What about picking without replacement without retaining order where n?k = (n+k-1)!/[(n-1)!k!]? -- ToE 21:20, 16 January 2017 (UTC)
 * . Pretty sure there isn't one 100% common and well-used term, though we can easily describe the situation. What the OP is asking about is a String_(computer_science), that's the only term for such a general thingy that can have numbers or letters, with repeats, drawn from a fixed set where order is important. The way I'd put this is "number of strings of length n formed from an alphabet of k symbols". In this sense of mathematics/computer science, "alphabet" is just a specific unsorted list of distinct symbols. SemanticMantis (talk) 21:55, 16 January 2017 (UTC)
 * Thanks, SM. Digging around, I've found the term "permutation with repetition", though problems may involve limits on the number of repetitions allowed.  See Permutation.  So the OP's use of "permutation" seems appropriate when the context is made clear.  Likewise, for picking with replacement without retaining order, "combination with repetition" is used, as in Combination and . -- ToE 16:58, 18 January 2017 (UTC)


 * Letters have lots of permutations - especially when they're alphanumeric and base ≈32 rather than 26 (it's common to avoid some, like 1/l and 0/O). Words, in contrast, for latin-derived languages have to limit themselves to pronounceable syllables, and that's far fewer combinations.
 * This became a problem for password cracking under VMS in the late MicroVAX era. DEC offered a "super-secret password generator" that generated unguessable passwords. To keep them pronounceable and memorable though, it generated them from a short dictionary of syllables. A few years later, and with more powerful non-VAX computers available, brute-force cracking became surprisingly easy on them. Andy Dingley (talk) 19:18, 13 January 2017 (UTC)


 * Is this 6-character limit factual for all airlines? ←Baseball Bugs What's up, Doc? carrots→ 19:59, 13 January 2017 (UTC)


 * The question talks about passenger name records, but what it's actually about is record locators. (The PNR is the data that the record locator is used to access.)  The article says that record locators are usually 6 characters, but it cites no sources and gives no further details. --69.159.60.210 (talk) 05:31, 14 January 2017 (UTC)

My best guess is that the data gets deleted after a certain amount of time (perhaps a few years). That would mean the PNR codes are reusable. They're unique at any given time, but not necessarily into eternity. Jahoe (talk) 00:51, 15 January 2017 (UTC)
 * and if they're not unique, never mind, they just bump somebody. Thincat (talk) 17:25, 15 January 2017 (UTC)


 * PNRs are purged from the system just a few days after the last segment of the trip took place, so yes, they can be reused quite often. Also, depending on the Global Distribution System used, the characters may or may not include numbers; for instance, Sabre (computer system) uses only letters. Apologies for not including references – this comes from my experience in the travel industry. FlyingAce (talk) 15:18, 16 January 2017 (UTC)