Quote of the Day

What is our intention for this meeting? What’s important? What matters?

— Oprah Winfrey. She starts every meeting with these three questions.

I have been tutoring math at the local library and using Excel as a vehicle for encouraging people to explore everyday math. While at the library, I heard a young man ask "How many Friday the 13^{ths} are in a year?" Since I am always looking for computational examples, I showed him how to use Excel to find the answer for himself. This post shows how I taught him to solve the problem. The solution turned out to be a good example of using Excel's date and array capabilities.

Figure 1 shows a simple table with the number of Friday the 13ths by year. I deliberately made the table 28 years per column to show that calendars repeat with a period of 28 years. I use this characteristic of calendars to buy old calendars that I can reuse; I love old Christmas and tool company calendars.

Figure 2 shows the Excel array formula I used to compute the number of Friday the 13^{ths}. My workbook is here.

Nice way of finding the number of Friday the 13ths in a year. Please share your workbook as my formula in a test workbook is not working. Thanks

Hi Ronan,

Sorry about forgetting the workbook. I just put it out there. This was a quick post before I started to get ready before Thanksgiving and was a bit rushed!

mark

Thanks