## Trick.docx - Section 3: A Little Trick

# Power to the 10! Conversions with the Metric System.

Lesson 2 of 5

## Objective: SWBAT convert metric units of measurement using ratio tables and move towards an understanding of multiplying and dividing by powers of 10 and how it applies to the metric system.

## Big Idea: Students will be using ratio tables to convert units of metric measurements and looking for patterns to help make the problems easier.

*80 minutes*

#### Do Now

*10 min*

**Students will be looking at the prefixes: milli, centi, kilo. Have the students look up the definition of these prefixes either in a dictionary, their textbook, or on line.**

Begin the lesson by reviewing the ratios that the students found from the exploration lesson called **Make mine metric. **Ask them to look for patterns in the ratios (looking for base 10 number system). Are there any patterns in the words? What is the difference between a milligram and a milliliter? How are they the same.

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The lesson begins by looking at the conversions for the metric unit of length. It might be helpful to have a meter stick available to show them the different conversions. Allow students to write down the conversions. The next slide shows how to use the ratio table to convert from millimeters to meters. **(SMP 5).**This is teacher directed only. After talking through the ratio table, allow students time to digest this and ask them if there is any other way to get to the same answer. Some students may see that they only needed to multiply by 1000 while others may see a different way of using the ratio table. Continue practicing using the ratio tables as guided practice. As you progress through the power points, the different metric units of measurement conversions are shown. After each unit of measure, ask the students if they notice any patterns?(**SMP 8)** The last slide of the power point is a short cut for students to use. However, I would not teach this right away as the goal of the lesson is get students to understand how the metric system uses the base 10 system no matter what we are measuring.

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#### A Little Trick

*10 min*

Slide 9: This slide shows a little trick to help understand the metric system. I would use this only for the students that are still struggling with the conversions. The slide shows the prefixes for the metric system. Have the students start on the prefix they are given. For example, if you have 48 mm and want to find out how many centimeters that is, you would start at the “m” farthest right. In order to get to centimeters, you would have to jump one space left. This means that you would move the decimal in 48, one place to the left. Answer 4.8 centimeters. You may have to remind students that the decimal in whole numbers is behind the one’s place. Otherwise, they would move the decimal that is already placed in the number.

This shortcut is nice for students who continue to struggle with conversions. However, I would encourage students to explore “why” this trick works. Again, our goal is to get the students to understand that the conversions for metric happen by multiplying or dividing by base 10.

Allow time for students to get a clear understanding of both the shortcut and the ratio table. It might be a good idea to have them work out both ways so they can see that they get the same answer.

#### Resources

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#### Conversions Round Table

*30 min*

After the direct instruction, have the students practice conversions on their own. You can use the metric **roundtable** activity to support this part of the learning. ** (SMP 3 and 6)**

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#### Lesson End

*10 min*

Make up your own metric conversion problem. Solve it two different ways. Explain to your shoulder partner what your strategy was for one of the problems. **(SMP 1 ,2 3)**

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