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Lesson Plan: Adding and Multiplying Decimals

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Lesson Plan: Adding and Multiplying Decimals
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Students will practice addition and multiplication with decimals, using holiday advertisements.

Class: Fifth Grade

Duration: 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.

Lesson Introduction: You will want to consider whether or not a lesson like this is appropriate for your class, given the holidays being celebrated and the socioeconomic status of your students. While fantasy spending can be fun, it can also be saddening for students who may not receive gifts or who struggle with great poverty.

If you have decided that your class will have fun with a project such as this, 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:

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 spend 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 at 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 5? 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 2 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 and you have time to devote to the project.

  11. Before leaving the class for the day, have students share their work so far, and provide feedback as necessary.

Homework/Assessment: 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.

Evaluation: 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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