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How many working days in year 1980?
Here is the detail of the calculation:
Because 1980 is a leap year, it has 366 days.
Let's remove 52 saturdays and 52 sundays. It remains 262 days.
Now, let's remove 11 public holidays that do not fall during a weekend and we obtain 251 working days in 1980.
 Here is the list of these 11 public holidays: 
 
 1. Año Nuevo : Tuesday, 1 January, 1980 
2. Epifanía del Señor : Monday, 7 January, 1980 
3. San José : Wednesday, 19 March, 1980 
4. Viernes Santo : Friday, 4 April, 1980 
5. Lunes de Pascua : Monday, 7 April, 1980 
6. Fiesta del Trabajo : Thursday, 1 May, 1980 
7. San Juan : Tuesday, 24 June, 1980 
8. Asuncíon de la Virgen : Friday, 15 August, 1980 
9. Día de la Comunidad Valenciana : Thursday, 9 October, 1980 
10. Immaculada Concepcíon : Monday, 8 December, 1980 
11. Día de Navidad : Thursday, 25 December, 1980 
And here are the 4 public holidays falling on a weekend:
1. Epifanía del Señor : Sunday, 6 January, 1980 
2. Fiesta nacional de España : Sunday, 12 October, 1980 
3. Todos los Santos : Saturday, 1 November, 1980 
4. Día de la Constitución Española : Saturday, 6 December, 1980