Many people would think Friday the 13th will be an unlucky day. Is it possible that there is no Friday on 13th through the whole year? How many Fridays at 13th can we have in a 年 at most? Can あなた calculate it out?
Friday falls on 13th at least once and a maximum of 3 times a year. This happens when a 月 starts with a Sunday. I don't think any calculation または a fact is involved here. または is it?