It was Monday on January 1, 2007. What was the day of the week on January 1, 2011?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Saturday
Step 1: Calculate the Number of Days/Years
The time period spans exactly 4 years: 2007, 2008, 2009, and 2010.
- 2007: Ordinary year (365 days) = 52 weeks + 1 odd day
- 2008: Leap year (366 days) = 52 weeks + 2 odd days
- 2009: Ordinary year (365 days) = 52 weeks + 1 odd day
- 2010: Ordinary year (365 days) = 52 weeks + 1 odd day
(Note: 2008 is a leap year because it is divisible by 4, meaning it includes February 29th.)
Step 2: Total Odd Days
Sum of odd days = $1 + 2 + 1 + 1 = \mathbf{5}$ odd days.
Step 3: Determine the New Day
Since we are moving forward in time, we add these 5 odd days to the starting day (Monday):
- Monday + 1 = Tuesday
- Monday + 2 = Wednesday
- Monday + 3 = Thursday
- Monday + 4 = Friday
- Monday + 5 = Saturday
The day of the week on January 1, 2011, was Saturday.