Once you know the day of the week for 3 January you know the day of the week for all these dates in the same year. In 2017 3 January is a Tuesday.

So let’s look at these key dates or 'doomsdays'. January and February stand alone and these are dates that just have to be remembered, but there are patterns and rules in the other dates that make them fairly easy to remember.

### So let’s give it a try.

*What day of the week is 18*

^{th}August 2017?⇒ August is month 8, an even month

⇒ so 8/8 is a Tuesday

⇒18

^{th}August is

**10 days after**Tuesday 8/8/17

⇒ 10 days = 1 week + 3 days

⇒ so one week after 8/8 is a Tuesday and 3 more days …Wednesday, Thursday,

**18**

__Friday__^{th}August 2017 is a Friday.

• These are all odd numbered months

• There is a difference of 4 between the day and the month in each date

In the first half of the year the difference is + 4

**month number + 4 = day**

In the second half of the year the diffference is - 4

**month number - 4 = day**

### So let's give it a try

*What day of the week is 2*

^{nd}November 2017?⇒ November is month 11, in the second half of the year, so – 4

⇒ 11 - 4 = 7 so 7/11 is a Tuesday in 2017

⇒ 2

^{nd}November is 5 days before 7/11.

⇒ Count 5 days back from Tuesday…. Mon, Sun, Sat, Fri,

**Thursday**2

^{nd}November 2017 is a Thursday.

**Extend the activity**

Some of your higher attaining children may want to have a look why this works. Why is it that these key dates or 'doomsdays' are on the same day of the week every year? Give them time, maybe over a week, to look at the dates on a calendar and see what they can notice.

If they can't find any connections then explain that it works because the number of days between these dates are divisible by 7, or to put another way, have whole weeks between them.

Don't leave it there - ask your class to prove it. Look at a 2017 calendar and count the weeks between each date. Count the number of days between any two dates and check if it is divisible by 7.

I have provided a simple way to find a date in 2017 but there are far more complicated ways to calculate the date for any year.

There is a version that you might be interested in for yourself and you can see John Conway explaining it on YouTube. However, this is quite complex so for your class you can stick to naming the day of the week for any date in 2017.

**Related articles**

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11.12.13 was a special date with consecutive numbers.

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This includes finding Fibonacci numbers in nature, exploring patterns and rules in number sequences, sunflowers and cones

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