Question

April 16, 2022 is Saturday what day of the week was it on 16 April 2021?

• A. Saturday
• B. Friday
• C. Monday
• D. Sunday

Hint:

When shifting exactly one year back or forward, the day shifts by 1 day (if no leap day is crossed) or by 2 days (if a leap day is crossed). Since neither 2021 nor 2022 are leap years, we simply shift back by exactly 1 day.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Calendar problems rely on counting the number of odd days.
An ordinary year contains 365 days, while a leap year contains 366 days.
Any day of the week repeats itself after every 7 days.
Key Formula or Approach:
The number of odd days in a time interval is calculated as: \[ \text{Odd Days} = \text{Total Days} \pmod 7 \] - An ordinary year has $365 \text{ days} = 52 \text{ weeks} + 1 \text{ day}$ (1 odd day).
- A leap year has $366 \text{ days} = 52 \text{ weeks} + 2 \text{ days}$ (2 odd days).

Step 2: Detailed Explanation:
The period in question is from April 16, 2021, to April 16, 2022.
Let us determine if this period contains the leap day (February 29):
- The year 2021 is a non-leap year.
- The year 2022 is a non-leap year.
- Hence, February 2022 has only 28 days.
Since the interval does not span across a February 29th leap day, the total number of days in this exact one-year period is 365 days.
Calculate the number of odd days: \[ 365 \pmod 7 = 1 \text{ odd day} \] Because we are moving backward in time (from April 16, 2022 to April 16, 2021), we subtract the odd day: \[ \text{Day on April 16, 2021} = \text{Day on April 16, 2022} - 1 \text{ odd day} \] Given that April 16, 2022, is a Saturday: \[ \text{Day on April 16, 2021} = \text{Saturday} - 1 = \text{Friday} \]

Step 3: Final Answer:
The day of the week on April 16, 2021, was Friday.