Short Trick for Breaking Year into Pieces
Duration: 6 min
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This educational video presents a method for determining the day of the week for a given date, focusing on the technique of breaking down the year into pieces. The instructor, Yash Jain Sir, introduces the concept with a question about the day of the week for March 12, 1922. The core method involves decomposing the year into its constituent parts: the number of centuries, the number of decades, and the remaining years. A table is displayed on the left, providing the number of odd days for different century blocks (e.g., 100 years = 5 odd days, 200 years = 3 odd days, 300 years = 1 odd day, 400 years = 0 odd days). The instructor demonstrates this by breaking 1921 into 1600 + 300 + 21, then calculating the odd days for each segment. This process is repeated for other dates, including July 17, 1863, January 7, 2022, October 22, 2597, October 22, 1198, and October 22, 772, to illustrate the consistent application of the method. The video concludes with a 'Thanks for Watching' screen.
Chapters
0:00 – 2:00 00:00-02:00
The video opens with a title slide for a lesson on 'CONCEPT OF BREAKING YEAR INTO PIECES'. The instructor, Yash Jain Sir, introduces the topic with a question: 'Which day lied on 12th March 1922?'. A table on the left lists the number of odd days for different century blocks: 100 years = 5, 200 years = 3, 300 years = 1, and 400 years = 0. The instructor begins to break down the year 1921 (the year before 1922) into 1600 + 300 + 21, writing '1921 = 1600 + 300 + 21' on the screen. The instructor explains that the number of odd days for 1600 years is 0, as 1600 is a multiple of 400, and the number of odd days for 300 years is 1, as per the table.
2:00 – 5:00 02:00-05:00
The instructor continues the calculation for the year 1921. He explains that 21 years consist of 5 leap years and 16 ordinary years, resulting in (5 x 2) + (16 x 1) = 26 odd days. He then calculates 26 mod 7, which equals 5, so 21 years contribute 5 odd days. The total odd days for 1921 are 0 (from 1600) + 1 (from 300) + 5 (from 21) = 6 odd days. The instructor then applies this to the date March 12, 1922, by adding the odd days from the year (6) to the days in the month (12), resulting in 6 + 12 = 18. He calculates 18 mod 7 = 4, which corresponds to Thursday. The instructor then moves to the next example, asking 'Which day lied on 17th July 1863?'. He breaks down 1862 into 1600 + 200 + 62, and calculates the odd days for each segment: 0 for 1600, 3 for 200, and 1 for 62 (since 62 years have 15 leap years and 47 ordinary years, totaling 15*2 + 47*1 = 77 odd days, and 77 mod 7 = 0). The total odd days for 1862 are 0 + 3 + 0 = 3. He then adds the days in July (17) to get 3 + 17 = 20, and 20 mod 7 = 6, which corresponds to Saturday.
5:00 – 6:06 05:00-06:06
The instructor proceeds to the next example: 'Which day lied on 7th January 2022?'. He breaks down 2021 into 2000 + 21. He states that 2000 years have 0 odd days (since 2000 is a multiple of 400), and 21 years have 5 odd days (as calculated earlier). The total odd days for 2021 are 0 + 5 = 5. He adds the days in January (7) to get 5 + 7 = 12, and 12 mod 7 = 5, which corresponds to Friday. He then moves to the next example: 'Which day lied on 22nd October 2597?'. He breaks down 2596 into 2400 + 196. He states that 2400 years have 0 odd days (since 2400 is a multiple of 400), and 196 years have 1 odd day (since 196 years have 49 leap years and 147 ordinary years, totaling 49*2 + 147*1 = 245 odd days, and 245 mod 7 = 0). The total odd days for 2596 are 0 + 0 = 0. He adds the days in October (22) to get 0 + 22 = 22, and 22 mod 7 = 1, which corresponds to Monday. The video ends with a 'Thanks for Watching' screen.
The video systematically teaches a method for calculating the day of the week for any given date by breaking the year into manageable pieces. The core concept is the use of 'odd days'—the remainder when the number of days in a period is divided by 7. The method relies on a pre-defined table for the number of odd days in century blocks (100, 200, 300, 400 years). The instructor demonstrates a consistent process: 1) Break the year into a sum of century blocks and a remainder (e.g., 1921 = 1600 + 300 + 21). 2) Use the table to find the odd days for each century block. 3) Calculate the odd days for the remaining years. 4) Sum the odd days from all parts of the year. 5) Add the number of days in the target month. 6) Divide the total by 7 and use the remainder to determine the day of the week. This structured approach is applied to multiple examples, reinforcing the technique.