March 5, 1999 was on Friday, what day of the week will be on March 5, 2000 ?

Key idea: find the number of days between the two dates and take that modulo 7 to see how many weekdays to advance.

• Remaining days in 1999 after March 5: 301 days. 301 ≡ 0 (mod 7).

• Days in 2000 up to March 5: January 31 + February 29 (leap year) + March 5 = 65 days. 65 ≡ 2 (mod 7).

• Total days between the dates = 301 + 65 = 366 days. 366 ≡ 2 (mod 7), so the weekday advances by 2 days.

• Starting weekday: Friday. Advance 2 days: Friday → Saturday → Sunday. Therefore the date is on Sunday.

Answer: Sunday.