Comments on: Mentally Calculate the Day of the Week for a Date http://pubcrawler.org/2006/11/02/mentally-calculate-the-day-of-the-week-for-a-date/ Living life forward and understanding it backwards Thu, 28 Aug 2008 18:39:14 +0000 http://wordpress.org/?v=2.6 By: jamin http://pubcrawler.org/2006/11/02/mentally-calculate-the-day-of-the-week-for-a-date/#comment-93530 jamin Wed, 20 Aug 2008 22:11:53 +0000 http://pubcrawler.org/2006/11/02/mentally-calculate-the-day-of-the-week-for-a-date/#comment-93530 Thyag, you could either memorize the list of month codes by brute force repetition, or you could use any number of mnemonics to associate the code with the month. I would use the <a href="http://wondr.net/2007/11/06/memory-month-day-6-the-phonetic-alphabet/" rel="nofollow">phonetic alphabet</a> and <a href="http://wondr.net/2007/11/07/memory-month-day-7-the-peg/" rel="nofollow">peg</a>. Thyag, you could either memorize the list of month codes by brute force repetition, or you could use any number of mnemonics to associate the code with the month. I would use the phonetic alphabet and peg.

]]> By: Thyag http://pubcrawler.org/2006/11/02/mentally-calculate-the-day-of-the-week-for-a-date/#comment-93189 Thyag Wed, 20 Aug 2008 09:35:44 +0000 http://pubcrawler.org/2006/11/02/mentally-calculate-the-day-of-the-week-for-a-date/#comment-93189 I have only one difficulty with the initial approach. Year codes are fine, but how to remember the month codes? That is my only concern. I have only one difficulty with the initial approach. Year codes are fine, but how to remember the month codes? That is my only concern.

]]> By: blogsci.com http://pubcrawler.org/2006/11/02/mentally-calculate-the-day-of-the-week-for-a-date/#comment-20756 blogsci.com Thu, 30 Nov 2006 22:28:51 +0000 http://pubcrawler.org/2006/11/02/mentally-calculate-the-day-of-the-week-for-a-date/#comment-20756 <strong>Mental Date Arithmetic...</strong> Ever wondered how to calculate the day of of the week for any date in the past or future? Turns out, it’s quite easy. Full details over here. Technorati Tags: arithmetic ...... Mental Date Arithmetic…

Ever wondered how to calculate the day of of the week for any date in the past or future? Turns out, it’s quite easy. Full details over here.
Technorati Tags: arithmetic
……

]]> By: laura http://pubcrawler.org/2006/11/02/mentally-calculate-the-day-of-the-week-for-a-date/#comment-15392 laura Thu, 09 Nov 2006 06:27:12 +0000 http://pubcrawler.org/2006/11/02/mentally-calculate-the-day-of-the-week-for-a-date/#comment-15392 where oh where are the halloween pictures? where oh where are the halloween pictures?

]]> By: jamin http://pubcrawler.org/2006/11/02/mentally-calculate-the-day-of-the-week-for-a-date/#comment-14384 jamin Fri, 03 Nov 2006 20:32:45 +0000 http://pubcrawler.org/2006/11/02/mentally-calculate-the-day-of-the-week-for-a-date/#comment-14384 Robin: nice observations, but I'm not sure I see how that allows you to easily calculate the day of the week for any arbitrary year. That would work well this year, or any other year you happen to know the key days of the month, but what if you wanted to calculate the day of the week for July 17, 1864? Maybe I'm missing something. I do realize that memorization of the key values can be troubling. I will write a separate article in the near future illustrating some techniques such as the "peg" which make the memorization much easier. It does take a bit of practice, of course. Robin: nice observations, but I’m not sure I see how that allows you to easily calculate the day of the week for any arbitrary year. That would work well this year, or any other year you happen to know the key days of the month, but what if you wanted to calculate the day of the week for July 17, 1864? Maybe I’m missing something.

I do realize that memorization of the key values can be troubling. I will write a separate article in the near future illustrating some techniques such as the “peg” which make the memorization much easier. It does take a bit of practice, of course.

]]> By: Robin Munn http://pubcrawler.org/2006/11/02/mentally-calculate-the-day-of-the-week-for-a-date/#comment-14381 Robin Munn Fri, 03 Nov 2006 20:03:00 +0000 http://pubcrawler.org/2006/11/02/mentally-calculate-the-day-of-the-week-for-a-date/#comment-14381 Eek! That's a whole bunch of numbers with no good mnemonic. It looks intimidating to me, and I'm *good* at mental math! How's it going to look to most people? I'd rather use the "key day per month" technique that relies on simple observation and a stunningly clever little mnemonic: Look at a calendar. Observe that April 4th (4/4), June 6th (6/6), August 8th (8/8), October 10th (10/10), and December 12th (12/12) are always the same day of the week, no matter what year it is. This year (2006), those dates are all Tuesdays. Next year (2007), they'll all be Wednesdays. In 2008, they'll all be Fridays. The mnemonic here is that the key day is the one whose number matches the month number for all the even-numbered months except February. (And February is *always* an exception anyway). Now observe that May 9th and September 5th are also the same day of the week (Tuesday, this year). July 11th and November 7th are also that same day of the week. That's 5/9, 9/5, 7/11, and 11/7, no matter whether you're using the day/month or month/day writing system. The mnemonic here is "a 9-to-5 job at 7/11". The key day in March is always March 7th, or if you prefer you can think of "March 0th" (the day before March 1st). That also helps you remember that... The key day of February is the last day of February: Feb. 29th in leap years, Feb. 28 in non-leap years. Finally, the key day of January is Jan. 4th in leap years, Jan. 3rd in other years. Leap years are divisible by 4, so that gives you a mnemonic for January. Now you know the day-of-week of one day in each month. In 2006, the following days are all Tuesdays: Jan. 3rd (non-leap, so not 4) Feb. 28th (last day of Feb.) Mar. 7th ("March 0th" plus 7) Apr. 4th (4/4) May 9th (5/9 or 9/5) June 6th (6/6) July 11th (7/11 or 11/7) August 8th (8/8) September 5th (9/5 or 5/9) October 10th (10/10) November 7th (11/7 or 7/11) December 12th (12/12) Now you know the day-of-week of one day of the month, the rest is a simple matter of adding or subtracting 7s and then counting. No complicated math necessary, just a couple of simple mnemonics. Eek! That’s a whole bunch of numbers with no good mnemonic. It looks intimidating to me, and I’m *good* at mental math! How’s it going to look to most people?

I’d rather use the “key day per month” technique that relies on simple observation and a stunningly clever little mnemonic:

Look at a calendar. Observe that April 4th (4/4), June 6th (6/6), August 8th (8/8), October 10th (10/10), and December 12th (12/12) are always the same day of the week, no matter what year it is. This year (2006), those dates are all Tuesdays. Next year (2007), they’ll all be Wednesdays. In 2008, they’ll all be Fridays. The mnemonic here is that the key day is the one whose number matches the month number for all the even-numbered months except February. (And February is *always* an exception anyway).

Now observe that May 9th and September 5th are also the same day of the week (Tuesday, this year). July 11th and November 7th are also that same day of the week. That’s 5/9, 9/5, 7/11, and 11/7, no matter whether you’re using the day/month or month/day writing system. The mnemonic here is “a 9-to-5 job at 7/11″.

The key day in March is always March 7th, or if you prefer you can think of “March 0th” (the day before March 1st). That also helps you remember that…

The key day of February is the last day of February: Feb. 29th in leap years, Feb. 28 in non-leap years.

Finally, the key day of January is Jan. 4th in leap years, Jan. 3rd in other years. Leap years are divisible by 4, so that gives you a mnemonic for January.

Now you know the day-of-week of one day in each month. In 2006, the following days are all Tuesdays:

Jan. 3rd (non-leap, so not 4)
Feb. 28th (last day of Feb.)
Mar. 7th (”March 0th” plus 7)
Apr. 4th (4/4)
May 9th (5/9 or 9/5)
June 6th (6/6)
July 11th (7/11 or 11/7)
August 8th (8/8)
September 5th (9/5 or 5/9)
October 10th (10/10)
November 7th (11/7 or 7/11)
December 12th (12/12)

Now you know the day-of-week of one day of the month, the rest is a simple matter of adding or subtracting 7s and then counting. No complicated math necessary, just a couple of simple mnemonics.

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