Bad Math

Over the last year, I have created a Diigo library bookmarking 200+ websites that I use and recommend to other teachers and parents. http://www.diigo.com/user/suedowning  I am especially interested in math tutorials and videos that students can use to supplement and expand on the math lessons in the classroom. The videos give struggling students the opportunity to explore difficult concepts and processes. They can stop and replay them. They can find varied explanations of the same thing, hopefully finding one that makes sense to them.

Most of the websites I bookmark come from blogs I follow. I always spend time exploring the content, trying out the games, and watching the videos before I create my bookmark. Today I discovered that I may need to make my investigation more thorough before accepting the information as useful and valid.

This morning, I found a collection of YouTube math tutorial videos made by a community of teachers. I watched several videos and was about to make a bookmark when I came across the Partial Products Algorithm video. I taught this method during my student teaching, so I took time to watch it. I was very disappointed.

The problem: 28 x 32

The explanation: multiply the ones, multiply the tens, add the 2 products

The final product: 616

I did write a comment asking them to recheck the math. I suggested they use all 4 partial products: 2 x 8, 2 x 20, 30 x 8, 30 x 20 = 16 + 40 + 240 + 600 = 896. I also mentioned that a quick estimation (30 x 30) should have indicated that the answer would be very close to 900.

Everybody makes mistakes, and quite a bit of our learning results from our mistakes. However, I think some form of quality control, such as peer review, should be performed before these videos are uploaded to the web.

Bad math is worse than no math at all. Now, I wonder if other websites I have recommended contain information that will confuse rather than clarify.