Calendar Questions

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fatbananas
Posts: 1411
Joined: Mon Mar 08, 2010 2:03 pm

Calendar Questions

Post by fatbananas »

Me again! Can you tell maths isn't my strong point?! :oops:

Can anyone tell me if there is a technique for finding out what date certain days of the week fall on. Eg, I am presented with the month for a certain year, say, July, and I have to find out when Christmas day happened that year, or when 31st Jan was etc etc.

I'm resorting to counting backwards or forwards in 7s but it seems enormously time-consuming (and I'm clearly failing in my accuracy as well ...) :roll: :oops:
Seize the day ... before it seizes you.
Okanagan
Posts: 1706
Joined: Mon Aug 22, 2011 9:20 pm
Location: Warwickshire

Re: Calendar Questions

Post by Okanagan »

If you are given a calendar for July you can see what day of the week July 25th is.
So add up the number of days in each month you need to move on by:
31 for July, 31 for August, 30 for September, 31 for October, 30 for November - total 153.
Divide by 7 to get weeks -> 21 remainder 6.
So 25th December will be the weekday before 25th July.

Remember to use the number of days starting from the first month (e.g. July), but not the last (e.g. December). In this case it is the same but it isn't always.

There is a formula (google "Zeller's Rule") but I'd suggest not even trying to memorise it. Adding up the month lengths and dividing by 7 is much simple and more appropriate for the type of question you have described!
southbucks3
Posts: 3579
Joined: Tue Dec 18, 2012 11:59 am

Re: Calendar Questions

Post by southbucks3 »

I just explained this clever trick to my dh, who replied. "I think I would just look it up on the calendar..I have plenty of other things in life I can do wrong"....bless him :P
fatbananas
Posts: 1411
Joined: Mon Mar 08, 2010 2:03 pm

Re: Calendar Questions

Post by fatbananas »

southbucks3 wrote:I just explained this clever trick to my dh, who replied. "I think I would just look it up on the calendar..I have plenty of other things in life I can do wrong"....bless him :P
:lol:

Thanks so much, Okanagan. Do these kinds of questions come up on GS 11+ papers? I've seen them on private school papers.
Seize the day ... before it seizes you.
SleepyHead
Posts: 484
Joined: Thu Oct 18, 2012 10:41 am

Re: Calendar Questions

Post by SleepyHead »

great trick - like it
Proud_Dad
Posts: 500
Joined: Fri Oct 11, 2013 9:55 am

Re: Calendar Questions

Post by Proud_Dad »

Okanagan wrote:If you are given a calendar for July you can see what day of the week July 25th is.
So add up the number of days in each month you need to move on by:
31 for July, 31 for August, 30 for September, 31 for October, 30 for November - total 153.
Divide by 7 to get weeks -> 21 remainder 6.
So 25th December will be the weekday before 25th July.

Remember to use the number of days starting from the first month (e.g. July), but not the last (e.g. December). In this case it is the same but it isn't always.

There is a formula (google "Zeller's Rule") but I'd suggest not even trying to memorise it. Adding up the month lengths and dividing by 7 is much simple and more appropriate for the type of question you have described!
A similar but slightly different way is to just add up the additional days above 28 that each month has (because 28 is an exact multiple of 7).

So using the same example that's - 3 for July, 3 for August, 2 for September, 3 for October, 2 for November - total 13.

That's 1 less than 14 (2 whole weeks) so any particular date in December will be 1 day of the week before the equivalent day in July for the same date.

Its essentially the same theory but perhaps slightly easier to do in your head because you only need to add up 3, 3, 2 etc rather than 31, 31, 30 etc, and also the final total of additional days, 13, is easier to compare against an exact mulitiple of 7 than 153 is.
parent2013
Posts: 452
Joined: Mon Aug 12, 2013 10:13 am

Re: Calendar Questions

Post by parent2013 »

My logic is that the questions are meant for 10 year old and the solution should also be simple and teachable. The calendar questions I have seen so far only jump 1 or 2 months (not >6).

The method I taught my ds is in line with Proud_Dad.
1. One should exactly know #days in every month without any doubts.
2. Skip 28 for full months and lesser (multiple of 7 for current month). Don't move the starting day.
3. Manual counting to next month
4. Manual counting for the last week to get the answer
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