If 1st is a Sunday, then 8th is also a Sunday because 8 = 1 + 7. Then 9th, 10th, 11th and 12th are respectively Monday, Tuesday, Wednesday and Thursday. Hence, 13th is Friday. If one considers ‘Friday, the 13th’ to be a bad omen, one should not be happy with the first day of the month being a Sunday, thus a holiday.