If 8th February 2005 was a Tuesday, then what was the day on 8th February 2003?

Concept: For two dates that are a whole number of years apart on the same day-month, the day of the week shifts forward by the count of "odd days" between them — the total number of days elapsed, taken modulo 7. An ordinary (non-leap) year contributes 1 odd day, since 365 = 52×7 + 1, and a leap year contributes 2 odd days, since 366 = 52×7 + 2, because it carries one extra day, 29 February.

1. The gap here is exactly two years: from 8 February 2003 to 8 February 2005.

2. 2004 is a leap year (divisible by 4), and its extra day, 29 February 2004, falls inside this gap — between 8 February 2004 and 8 February 2005.

3. So the first year of the gap (8 Feb 2003 → 8 Feb 2004) is an ordinary 365-day year, and the second year (8 Feb 2004 → 8 Feb 2005) is the 366-day leap year that includes 29 February 2004.

4. Total days elapsed = 365 + 366 = 731. Odd days = 731 mod 7 = 3, since 7 × 104 = 728 and 731 − 728 = 3.

5. The weekday therefore advances by exactly 3 across the gap: (day of 8 Feb 2003) + 3 = (day of 8 Feb 2005) = Tuesday, so the day of 8 Feb 2003 = Tuesday − 3 = Saturday.

Cross-check: starting from Saturday and stepping forward 3 odd days gives Saturday → Sunday → Monday → Tuesday, which reproduces the given Tuesday for 8 February 2005, confirming the result.

Hence, 8 February 2003 was a Saturday.