It was Sunday on Jan 1, 2006. What was the day of the week Jan 1, 2010?SundaySaturdayFridayWednesday

Step 1: Break Down the Problem

To find the day of the week for January 1, 2010, we need to calculate the number of days between January 1, 2006, and January 1, 2010, and then determine how many weeks this period contains.

Step 2: Relevant Concepts

1. Leap Years: A leap year occurs every 4 years except for end-of-century years, which must be divisible by 400.

   • The year 2006: not a leap year
   • The year 2007: not a leap year
   • The year 2008: a leap year
   • The year 2009: not a leap year

2. Days in each year:

   • 2006: 365 days
   • 2007: 365 days
   • 2008: 366 days (leap year)
   • 2009: 365 days

Step 3: Analysis and Detail

1. Calculate total days from 2006 to 2009: $\text{Total days} = 365 + 365 + 366 + 365 = 1461 \text{ days}$

2. Calculate the number of weeks from total days: $\text{Number of weeks} = \frac{1461}{7} \approx 208 \text{ weeks and } 5 \text{ days}$

3. Determine the day of the week: Since January 1, 2006, was a Sunday, we add 5 days to Sunday:

   • Sunday (0 days)
   • Monday (1 day)
   • Tuesday (2 days)
   • Wednesday (3 days)
   • Thursday (4 days)
   • Friday (5 days)

Step 4: Verify and Summarize

We verify that moving forward 5 days from Sunday indeed results in Friday.

Final Answer

January 1, 2010, was a Friday.