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Friday, January 11, 2013

Multiplying and Dividing by Powers of Ten

I thought it was about time I posted a Math lesson! The following is a lesson on multiplying by powers of ten. It can be used with whole numbers or decimals. With my students, I worked on multiplying both whole numbers and decimals by powers of ten.

Perhaps many of you have heard the popular saying "MR. DL?" Most teachers at my school use this phrase when teaching multiplication with powers of ten. It is actually an acronym that stands for Multiplication Right, Division Left. In other words, when you multiply a number by a power of ten, you move the decimal to the right, and when you divide by a power of ten, you move the decimal to the left.

To help my students with moving their decimals, I made boxes for students to put each digit in.

First, I gave students a number. (In this case 3.792) Students wrote the number on their paper with one digit in each box. Then, I told students whether we would be multiplying or dividing and by what power of ten. Students circled the correct operation and power of ten on their paper. Next, students "scooped" the decimal places the decimal would be moving. Since we were multiplying by 100 in this example, the students moved the decimal point two places to the right. Lastly, students wrote the final answer on their paper. (379.2)

Our math intervention groups change every two weeks. Each intervention teacher is given a particular skill, and students are assigned to groups based upon which skills they need help with. I love having a variety of skills and students, but sometimes it is difficult to figure out what is giving the students trouble if you have never had them in class before. With my group, I quickly noticed that they were weak in place value. The boxes provided additional scaffolding and a visual reminder that one digit goes in each place value spot.

I made a copy of the graphic organizer (shown above) for each student and laminated the paper so that we could use it over and over with dry erase markers. Initially I came up with the problems, but then let students take turns coming up with problems. They loved trying to stump their classmates.

A copy of the graphic organizer can be found by clicking on the picture below.

I would highly recommend laminating the paper so that it can be used with dry erase markers. Everything seems to be more fun with dry erase markers. Enjoy!

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