Years that start on Friday: for common years, August will start on Sunday and you'll have only 1; for leap years, May will start on Sunday and you'll also have only 1. (43 x 1) + (15 x 1) = 58. read more
On average, every seventh month. Or (always on average) 12/7 times a year (1.71), or 171.4 times per century. Every month, there is a 13th. It must fall on one day of the week. There are seven days in a week and Friday is one of them. read more