What was day of the week on 21 September, 1987 ?

Correct option is D

1. Determine the Century Code:

• The century code for the 20th century is 6.

2. Determine the Year Code:

• Divide the last two digits of the year by 4 and discard the remainder.
  • 87 / 4 = 21 (discard the remainder)
• Add the result to the last two digits of the year.
  • 87 + 21 = 108
• Divide the sum by 7 and find the remainder.
  • 108 / 7 = 15 with a remainder of 3
• The year code is 3.

3. Determine the Month Code:

• September's month code is 6.

4. Determine the Date Code:

• The date code is the day of the month.
  • 21

5. Calculate the Total:

• Add the Century Code, Year Code, Month Code, and Date Code.
  • 6 (Century) + 3 (Year) + 6 (Month) + 21 (Date) = 36

6. Determine the Day of the Week:

• Divide the total by 7 and find the remainder.
  • 36 / 7 = 5 with a remainder of 1
• 0 = Sunday, 1 = Monday, 2 = Tuesday, 3 = Wednesday, 4 = Thursday, 5 = Friday, 6 = Saturday
• Since the remainder is 1, the day of the week on September 21, 1987 was Monday.