Madmathteacher EduBlog

I copied this post and its comments from the old blog location at Wordpress:

Here’s my (pathetic?) decimal rap:

To add decimals, you draw a line.
To divide, you move it out.
Subtract, you also draw a line.
Multiply, you have to count.

I’m pretty sure you can do better. Your assignment? Make up your own song or rap that tells how to add, subtract, multiply, and divide decimals, and post it here as a comment. Remember my post “Wrapping up decimals” — it has the key ideas that need to be included in your song or rap. If you have a different idea (other than a song or rap) for a creative way you’d like to show your learning about decimal operations, please ask me about it at school or through e-mail, and I’ll be glad to accommodate you!

We’re almost done with our study of decimals. We’ve learned that:

1. when we compare, order, add, subtract, and divide decimals:
   • we always line up the decimal points
   • if needed, we add extra zeros after the decimal point (at the end of the number) to make the problem easier for our brains to understand
   • for division only, if there’s a decimal point in the divisor (the outside number in long division), we move that to the end to make it a whole number, and move the inside decimal the same amount.
2. when we multiply decimals:
   • the decimal points will never line up unless we have only whole numbers
   • instead of lining up decimal points, we actually multiply just like with normal whole numbers, ignoring the decimals until the end of the problem
   • remember at the very end of the problem to count decimal places - the number of places in your answer must be the same as the total number of places you counted in your factors.