Question

Dear Mitch.

A couple of days ago you answered a request for something unusual for This Friday, which is the anniversary of George Washington' birthday. I liked the idea and am going to try it with my seventh and eighth grade math classes today. I was just curious, though, when you finished your response you ended with the tagline: "To be continued..."

I've been checking and haven't noticed anything following it up. Is it still possible to post what you had planned on posting in your part 2 of that response?

Either way, thank you for all the effort that is always so evident in your fully developed responses.

Mrs. M

Los Angeles, CA

Answer

Dear Mrs. M,

Sure!

Picking up where I left off, you can continue the same U.S. currency dollar bill activity involving estimation, this time with the small collection of star-like designs neatly arranged in the sunburst-style shield above the eagle's head.

Then, after students' estimates are recorded, you should provide some form of an enlarged blow-up of that image. The students will discover that there are 13 separate stars – but, the more interesting part is to have them explain how the artist managed to make a prime number (13) into what appears to be a basically symmetric, well-balanced, and 'even-looking' arrangement. Have the students study the image to decide how many different lines of symmetry can be drawn; some responses might surprise you.

Copy a bill's serial number onto the board. (It's the green number that is the same on the left side as the right side of the 'front' (the surface with Washington's portrait). Using that multi-digit number (omitting the letter(s) appended to it), ask if that number is divisible by two, and/or three, and/or four, and/or five, and/or six, and/or seven, and/or eight, then nine and ten. Review the divisibility tests. The one for seven is one of the lesser-known ones, but it always proves of interest to students. (If you are unfamiliar with it, feel free to email me again, and I will go over the steps for that test here on Adler-n-subtract.com).

Finally, convincing the class with as serious a demeanor as you can muster, explain that everything on the front of the bill is drawn to scale. Therefore, using an average person's head-size for Washington's, have them figure out the size of the letters that form the words on the bottom: "ONE DOLLAR".

Hope this helps!

Have fun,

Mitch