Short Trick Find Day on a Particular Date

Duration: 8 min

This video lesson is available to enrolled students.

Enroll to watch — TCS SuperSet Course

AI Summary

An AI-generated summary of this video lecture.

This video is a tutorial on solving calendar-based aptitude questions, specifically determining the day of the week for a given date. The instructor, Yash Jain, uses a step-by-step method involving the division of the year into its constituent parts (thousands, hundreds, tens, and units) and applying a formula to calculate the total number of odd days. The process begins by breaking down the year 1987 into 1600 + 300 + 80 + 7. The number of odd days for each component is determined using a provided table: 1600 years contribute 0 odd days, 300 years contribute 1 odd day, 80 years contribute 2 odd days, and 7 years contribute 1 odd day. The sum of these odd days (0 + 1 + 2 + 1 = 4) is then used to find the day of the week. The instructor then adds the number of days in the months preceding September (January to August) and the days of September itself, calculating the total number of days. This total is divided by 7, and the remainder is used to determine the final day of the week, which is concluded to be Monday. The video also includes a second example for the date 22 October 1964, demonstrating the same method. The video concludes with a 'Thanks for Watching' screen.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The video opens with a title card showing a calendar and the word 'CALENDAR'. It then transitions to a lecture format with a blackboard background. The main question is displayed: 'On what day does 28 September 1987 lie?'. A table on the left lists the number of odd days for different century years (100, 200, 300, 400, etc.). The instructor begins the solution by writing '1987' on the board and starts to break it down into its components: 1600 + 300 + 80 + 7. He explains that the number of odd days for 1600 years is 0, and for 300 years is 1, referencing the table.

  2. 2:00 – 5:00 02:00-05:00

    The instructor continues the calculation for 1987. He writes '80' and calculates the number of odd days for 80 years, which is 2. He then writes '7' and calculates the odd days for 7 years, which is 1. He adds these values: 0 (from 1600) + 1 (from 300) + 2 (from 80) + 1 (from 7) = 4. He then moves to the months, writing 'Jan -> 31', 'Feb -> 28', 'Mar -> 31', 'Apr -> 30', 'May -> 31', 'Jun -> 30', 'Jul -> 31', 'Aug -> 31'. He adds these days: 31+28+31+30+31+30+31+31 = 243. He then adds the 28 days of September, resulting in a total of 243 + 28 = 271 days. He writes '271' and begins to divide it by 7.

  3. 5:00 – 7:41 05:00-07:41

    The instructor completes the division of 271 by 7, writing '271 / 7 = 38 weeks and 5 odd days'. He then adds the 4 odd days from the year calculation to the 5 odd days from the month calculation, resulting in a total of 9 odd days. He divides 9 by 7, getting a remainder of 2. He states that 0 corresponds to Sunday, 1 to Monday, and 2 to Tuesday. However, he then corrects himself, stating that the remainder 2 corresponds to Monday. He then moves to the second question: 'On what day does 22 October 1964 lie?'. He breaks down 1964 into 1600 + 300 + 60 + 4. He calculates the odd days for 1600 (0), 300 (1), 60 (2), and 4 (1), summing to 4. He then adds the days of the months from January to September (31+29+31+30+31+30+31+31+30 = 274) and the 22 days of October, totaling 296. He divides 296 by 7, getting a remainder of 1. He adds this to the 4 odd days from the year, getting 5. He divides 5 by 7, getting a remainder of 5, which he states corresponds to Friday. The video ends with a 'Thanks for Watching' screen.

The video presents a structured, step-by-step method for solving calendar problems. The core concept is the calculation of 'odd days'—the remainder when the number of days in a period is divided by 7. The method involves breaking down the year into its constituent parts (1600, 300, 100, 10, 1) and using a table to find the number of odd days for each. These are summed, and then the number of days from the beginning of the year to the target date is added. The total is divided by 7, and the remainder determines the day of the week. The video demonstrates this process for two different dates, 28 September 1987 and 22 October 1964, reinforcing the method through repetition and application.