Impress Your Friends: Name the Day of the Week For Any Date!

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What would your friends think of you if you were able to say which week day was their birthday, just by hearing the date? That you are a genius! This post will teach you how to do it, while you train your working memory, and your mnemonics skills.

Note

This is the first post of a series that will make you train your memory with the purpose to impress friends and family. So, even if you don’t learn anything directly useful you will learn something to be the center of attention of any reunion. You will train your brain and learn something useful for your social image.

For more posts of this series, look for the category Impress!

Imagine yourself surrounded of your friends at a party or reunion. You decide that it is time to take social profit of your currently upgraded brain. But what to show and how? You may have already impressed them by having called by their names all the new people you met. Let’s take it to the next level. Let’s demonstrate that you can recall the week day for any date. And if any date is possible for this public demonstration, why not the birthdate of that pretty lady over there 😉 …

The Technique

In order to be able to recall the week day, you will have to make use of your already developed mental skills:

  • Mental math
  • Mnemonics memorization

We will use similar techniques to the ones described on those posts. So if you do not know them, you may better start by learning them. It is not mandatory, but it will definitely help you get the following technique faster.

The first step is to get the date. You may ask for the birthday of that pretty person, or her daughter’s.  In case nobody wants to say their birthday date you can ask for any date they may be interested, like for example the landing at the moon, their first kiss, the assassination of Kennedy  or something similar.

Let’s say, the date is 12th November of 1971

Next step is to decompose the date. You got the day, the month and the year. Additionally, you need to know the century. That’s a total of four number. You will have to process each number in your mind in a different way.

For the example, we have the following data:

  • Day: 12
  • Month: November
  • Year: 71
  • Century: the 1900

To process the day, just mentally subtract 7 to the day several times until the resulting number is lower than 7 (between 0 and 6). That will be the day_result.

In our example:

12 – 7 = 5 -> day_result = 5

To process the month, you must remember a number associated to each month. Each month has its own specific number associated, without any particular reason (just a math reason). So the best thing is to learn using mnemonics the number associated to the months. The list of associated numbers is as follows:

  • January = 1
  • February = 4
  • March = 4
  • April = 0
  • May = 2
  • June = 5
  • July = 0
  • August = 3
  • September = 6
  • October = 1
  • November = 4
  • December = 6

The associated number for a given date is called the month_result.

In our example, the month_result is 4

Then it is time to process the year. The year is a number between 00 and 99. For each number there is also an associated number.  The associated number for each year is given by the following table, that you must memorize.

Year
00
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
Associated
Number
0
1
2
3
5
6
0
1
3
4
5
6
1
2
3
4
6
0
1
2
Year
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
Associated
Number
4
5
6
0
2
3
4
5
0
1
2
3
5
6
0
1
3
4
5
6
Year
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
Associated
Number
1
2
3
4
6
0
1
2
4
5
6
0
2
3
4
5
0
1
2
3
Year
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
Associated
Number
5
6
0
1
3
4
5
6
1
2
3
4
6
0
1
2
4
5
6
0
Year
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
Associated
Number
2
3
4
5
0
1
2
3
5
6
0
1
3
4
5
6
1
2
3
4

There are several ways for you to learn this table, but are out of the scope of this post. Figure out by yourself or write me an email asking me about it. In any case you must know for each two digits year, which associated number corresponds. That is what we call the year_result.

For the year 71 corresponds year_result = 4

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The process of the century requires a little more of work. You need to learn also a table by memory, but actually, there are two different tables: one for dates until the 18th century (1700s), and another for dates after that century.

Table 1

1700s – 1                  1200s – 6                 700s   – 4                  200s  – 2

1600s – 2                 1100s – 0                 600s   – 5                   100s  – 3

1500s – 3                 1000s – 1                 500s   – 6                   000s  – 4

1400s – 4                 900s   – 2                400s   – 0

1300s – 5                 800s   – 3                 300s   – 1

Table 2

1700s – 4                 2000s – 6                2300s – 0                   2600s – 2

1800s – 2                 2100s – 4                2400s – 6                   2700s  – 0

1900s – 0                 2200s – 2                2500s – 4                   ….

As you can see, the 1700s century is in both tables. You should use the first table for dates before September 14th 1752 you should use the first table. For posterior dates, use the table 2. The result of this table will be called the century_result.

Again, there is a pattern in the tables that you can take profit to easier memorization. To discover it is your homework.

In our example, the century_result is 0.

Putting all together

Now, for the final step. To calculate the day, first add all the results obtained up to now. Then, subtract 7 to that total, as many times as the result is above 6. Reached that point, the resulting number will be between 0 and 6. To identify the week day, just match that number to the following table:

0. Saturday

1. Sunday

2. Monday

3. Tuesday

4. Wednesday

5. Thursday

6. Friday

The total in our example is:

day_result + month_result + year_result + century_result = 5 + 4 + 4 + 0 = 13

Subtracting 7 only once: 13 – 7 = 6

Then the corresponding week day was Friday

Screen Shot 2014-10-01 at 15.02.57

 

The Workout

Now, before you are able to perform mentally with this trick, you need to train. First, you must memorize the tables above. Use any of the memorization techniques described in this web site or just use rote memory.

Then, once you have mastered the tables, you need to practice the whole technique. Do the following workout for 5 minutes every day until you feel comfortable. Remember that been constant is more important than longer training times.

Screen Shot 2014-10-01 at 14.50.18

Workout

  • Visit this web page  that allows you to generate random dates
  • Fill the form on the page that allows you to generate the dates within certain parameters. Select 10 dates, from year 100, all week days, and the format that suits you the best.
  • Then generate the dates.
  • Apply the technique for each date and write down the day. Then visit this website and check if your answer was correct.

Conclusion

Now it is your turn to impress your friends with your newly learned brain techniques. Please share your experience with us!

photo credit: pepe50 via photopin cc

2 Responses to Impress Your Friends: Name the Day of the Week For Any Date!

  1. Ahmad 03/10/2014 at 14:05 #

    Hi,
    Thanks for this post.
    is there any way to use similar technique for Solar Hijri calendar?

    • Rick T. 03/10/2014 at 15:47 #

      Hi Ahmad.

      Now that’s a challenge!! I’m sorry but haven’t heard of this calendar. However, I am sure that there should be a similar approach for that calendar, since calendars are based on the movement of the Sun or the Moon, and both of them follow a mathematical rule, that can be implemented using tables and memory.

      If you feel brave, you can figure it out by yourself, applying the same methodology teach along this website. It would be a good exercise for your brain.

      In any case, I’ll have a look and post what I find.

      Best

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