If 26 September 2005 was Monday, then what was the day of the week on 26 September 2017?

The correct option is Tuesday.

To find the day of the week on 26 September 2017 when 26 September 2005 was a Monday, we calculate the total number of odd days between these two dates.

Step 1: Calculate the total number of years
From 26 September 2005 to 26 September 2017, the time difference is:
2017 - 2005 = 12 years.

Step 2: Identify normal years and leap years
A normal year has 365 days, which gives 1 odd day (since 365 divided by 7 leaves a remainder of 1).
A leap year has 366 days, which gives 2 odd days (since 366 divided by 7 leaves a remainder of 2).

The leap years between 26 September 2005 and 26 September 2017 are:
2008, 2012, and 2016.
So, there are 3 leap years in this period.

The number of normal years is:
12 - 3 = 9 normal years.

Step 3: Calculate total odd days
Odd days from 9 normal years = 9 × 1 = 9 odd days.
Odd days from 3 leap years = 3 × 2 = 6 odd days.

Total odd days = 9 + 6 = 15 odd days.

Now, divide 15 by 7 to find the net odd days:
15 ÷ 7 = 2 weeks and 1 remainder (1 odd day).

Step 4: Determine the target day
Adding 1 odd day to Monday gives Tuesday.

Therefore, 26 September 2017 was a Tuesday.