To find the day on 1st February 2010, given that 1st February 2016 was Monday, we need to calculate the total number of days between these two dates and then find the number of odd days. We will count the days from 1st February 2010 to 1st February 2016.

The period spans 6 years: 2010, 2011, 2012, 2013, 2014, 2015. We are looking at the interval from 1st Feb of the starting year to 1st Feb of the ending year.

1. Count normal years and leap years:

   • A normal year has 365 days.
   • A leap year has 366 days (due to February 29th).

   The leap year in this period is 2012. The 29th of February 2012 falls within the period from 1st February 2012 to 1st February 2013, so it adds an extra day. The year 2016 is a leap year, but its February 29th falls after 1st February 2016, so it does not affect the count for the interval ending on 1st February 2016.

   • Years considered as normal years (365 days): 2010, 2011, 2013, 2014, 2015 (5 years).
   • Year considered as a leap year (366 days): 2012 (1 year).

2. Calculate the total number of days: Total days = (Number of normal years × 365) + (Number of leap years × 366) Total days = (5 × 365) + (1 × 366) Total days = 1825 + 366 Total days = 2191 days.

3. Calculate the number of odd days: Odd days are the remainder when the total number of days is divided by 7 (since there are 7 days in a week). Odd days = 2191 ÷ 7 2191 = 7 × 313 + 0 So, the number of odd days is 0.

4. Determine the day of the week: Since the number of odd days is 0, it means that the day of the week repeats exactly after this period. We are going backward from 1st February 2016 to 1st February 2010. If 1st February 2016 was Monday, and there are 0 odd days when going backward, then 1st February 2010 must also be Monday.

Therefore, 1st February 2010 was a Monday.