Lesson Plan: Adding and Multiplying Decimals

Lesson Preparation

The lesson will span the duration of two class periods, about 45 minutes each.

Materials:

• Advertisements from the local paper, or if you prefer a technology focus, a list of websites for common department stores
• Centimeter graph paper

Key Vocabulary: add, multiply, decimal place, hundredths, tenths, dimes, pennies

Objectives: In this lesson, students will add and multiply with decimals to the hundredths place.

Standards Met: 5.OA.7: Add, subtract, multiply, and divide decimals to hundredths, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used.

Before Starting

Consider whether or not a lesson like this is appropriate for your class, given the holidays they celebrate and the socioeconomic status of your students. While fantasy spending can be fun, it can also be upsetting for students who may not receive gifts or who struggle with poverty.

If you have decided that your class will have fun with this project, give them five minutes to brainstorm the following list:

• Three things I want to receive
• Two things I want to give
• One thing I would like to eat

Adding and Multiplying Decimals: Step-by-Step Procedure

1. Ask students to share their lists. Ask them to estimate the costs involved in purchasing all of the things they want to give and receive. How could they figure out more information about the costs of these products?
2. Tell students that today’s learning target involves fantasy shopping. We will begin with \$300 in make-believe money and then calculate all that we could purchase with that amount of money.
3. Review decimals and their names using a place value activity if your students haven’t discussed decimals for awhile.
4. Pass out advertisements to small groups, and have them look through the pages and discuss some of their favorite things. Give them about 5-10 minutes just to peruse the ads.
5. In small groups, ask students to make individual lists of their favorite items. They should write the prices next to any item they choose.
6. Begin modeling the addition of these prices. Use graph paper in order to keep the decimal points lined up correctly. Once students have had enough practice with this, they’ll be able to use regular lined paper. Add two of their favorite objects together. If they still have enough fantasy money to spend, allow them to add another item to their list. Continue until they have reached their limit, and then have them assist other students in their group.
7. Ask for a volunteer to tell about an object that they chose to purchase for a family member. What if they then needed more than one of these? What if they wanted to purchase five? What would be the easiest way for them to figure this out? Hopefully, students will recognize that multiplication is a much easier way of doing this than repeated addition.
8. Model how to multiply their prices by a whole number. Remind students about their decimal places. (You can assure them that if they forget to put the decimal place in their answer, they will run out of money 100 times faster than they ordinarily would!)
9. Give them their project for the rest of class and for homework, if necessary: Using the list of prices, create a family present package worth no more than \$300, with several individual gifts, and one gift that they have to purchase for more than two people. Make sure they show their work so that you can see their examples of addition and multiplication.
10. Let them work on their projects for another 20-30 minutes, or however long they are engaged with the project.
11. Before leaving the class for the day, have students share their work so far and provide feedback as necessary.

Concluding the Lesson

If your students aren't done but you feel that they have enough understanding of the process to work on this at home, assign the remainder of the project for homework.

As students are working, walk around the classroom and discuss their work with them. Take notes, work with small groups, and pull aside students who need help. Review their homework for any issues that need to be addressed.

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