How many friday the 13Th's are there in a year, whats the mean average?

Question

How many friday the 13Th's are there in a year, whats the mean average?

Answer 1

Go, and get a calendar!

Go and figure it out yourself.

Don't be lazy.

Answer 2

Well, this year (2008) there's one, but next year there's apparently going to be three.

I can't give you an average, but I can say that the number of Friday the 13th's changes each year.

Answer 3

The days of the week for a given date shift by one (e.g. a Tuesday becomes a Wednesday) for normal years and by two (e.g. a Tuesday becomes a Thursday) if there is an intervening 29th February... The full

calendar therefore recycles every 28 years (i.e. 2008 is the same as 2036).

Over the full cycle there are 48 Friday the 13ths:-

Every year has at least one Friday the 13th,

There are 12 years with only one Friday the 13th,

There are 12 years with two Friday the 13ths,

Finally there are four years with three Friday the 13ths...

The average is 48/28 = 1.714 Friday the 13ths each year