koreanfestivals1-2, Exercise 1: Lunar holidays

Model answer:

Seollal: 1st day of the 1st lunar month; 3 days off.
Buddha's Birthday: 8th day of the 4th lunar month; 1 day off.
Chuseok: 15th day of the 8th lunar month; 3 days off.

The solar date changes because these holidays follow the lunisolar calendar, which has lunar months and leap months added every two or three years, so the date drifts against the Gregorian calendar.

Example (any one): Seollal, 22 January (2004, 2023, 2042) to 19 February (1996, 2015, 2034); Buddha's Birthday, 30 April (2020, 2039) to 28 May (2012, 2031, 2050); Chuseok, 8 September (2014, 2033) to 6 October (2006, 2025).

Source: Wikipedia, Public holidays in South Korea (table of solar dates); Korean calendar.