CD’s on a Desk

A few weeks ago, I asked the students to figure out how many CD’s it would take to cover their four-desk pod. I didn’t tell them anything more than that.

How would you solve that problem?

I was very impressed with what I saw.

1. The questions: Do we need to cover the whole pod? Can they overlap? Can they hang off the edge? What if there are little bits of desk showing through? (Excellent questions because they all change “the answer”.)

2. The methods: All began by measuring their desks. Some chose to leave length and width separate, some chose to multiply into area. Some researched the dimensions of the CD and had to decide how they were going to use it.

3. The answers: There were several recurring ranges of answers, but in terms of the numbers, there were probably 15 different final answers and the students were okay with that considering the assumptions were different.

All of that reflects a TON of great math thinking and problem-solving, but the most convincing solution to many of the students was arguably the simplest. (Isn’t it always that way?)

Here is a photo of the solution:

Photo Credit: Heather Roadcap – Used with permission

The solution: Get a CD, trace it carefully, and count. Can you argue with that?

There’s always a reason…

Photo Credit: Flikr user “Jan Tik” – some rights reserved

A many years to Michael Benson, author of “Mystery Master,” for making my job as the teacher of reasoning a heck of a lot easier.

Math and logic can be daunting (or at the very least, boring), but in the last week, my use of the Benson’s logic puzzles (found at has allowed for a lot of good conversation about how deductive reasoning (following factual guidelines to build logical conclusions) differs from inductive reasoning (basing conjectures on perceived patterns of specific examples, events or cases).

The puzzle that we solved as a class was “A Day at the Zoo“. Check it out and give it a try. There are lots of much more challenging ones on Benson’s website.

Put your experiences in the comments and if you find one that thegeometryteacher absolutely MUST try, then post it.