1. Multiplying Decimals by Decimals Alignment Lesson

2. Today’s Objective Students will be able to: explain how to multiply a decimal by a decimal using an area model.

3. Multiplying Decimals by Decimals Let’s view a video showing how to multiply a decimal by a decimal (2.4 x 1.3 = ?) using an area model Multiplying whole numbers and decimals- using-an-area-model Multiplying whole numbers and decimals- using-an-area-model

4. Let’s Review…. Arrays

5. Rectangular Arrays Let’s say you have decided to create a miniature movie theatre in your house. You place 3 rows of chairs with 5 chairs in each row. Use colored tiles to design your movie theatre on your desk. How many people can your movie theatre seat? What array have you created? Remember an array is items arranged in rows and columns. 3 rows and 5 columns = 15

6. Use Rectangular Arrays to Help Solve… Create an array to solve 2 x 6. 2 rows and 6 columns = 12 OR 6 rows and 2 columns = 12 Create an array to solve 1 x 5 1 row and 5 columns = 5 OR 5 rows and 1 column = 5 We can use arrays to help use solve multiplication problems. Today we will use arrays to help us multiply decimals!

7. We are now going to use the two strategies we have just reviewed to solve some multiplication problems. Strategies: » Rectangular Arrays » Area Model

8. Find Day 60, “Multiplying Decimals by Decimals” Scenario 1 Kendall is filling 4.5 ounce bottles with a bubble solution for her party. She was able to fill 3.5 bottles. How many ounces of bubble solution did she make? Use what they know about decimals to estimate how many ounces of bubble solution Kendall made. What multiplication sentence is represented by the problem? Write the sentence horizontally on the your paper. (4.5 x 3.5).

9. Solving using Rectangular Arrays – 1 st Strategy Create a 4.5 by 3.5 array (overlapping square is purple because it is shared by 4.5 and 3.5 )

10. Solving using Rectangular Arrays – 1 st Strategy Next you are going to fill in the array with appropriate base ten pieces that fit First, I will fill in the flats (or wholes) Second I will fill in the rods (or tenths) in appropriate spaces Third, I will fill in the bits (or hundredths)

11. Solving using Rectangular Arrays – 1 st Strategy Lastly, you will count up the number of wholes, tenths and hundredths you have to find your answer. 12 wholes 35 tenths 25 hundredths 25 hundredths = 2 tenths and 5 hundredths So now I have: 12 wholes 37 tenths 5 hundredths 37 tenths = 3 wholes and 7 tenths So now I have: 15 wholes 7 tenths 5 hundredths Product: 15.75

12. Solve 4.5 x 3.5 Using Area Model First create 4.5 using base ten pieces 4.5

13. Solve 4.5 x 3.5 Using Area Model Next use base ten pieces to create 3.5 in the same box 4.5 3.5

14. Solve 4.5 x 3.5 Using Area Model Next use base ten pieces to create 3.5 in the same box 3.5 4.5 RED Square = 4 x 3 = 12 4 0.5 + 3 + PURPLE = 0.5 x 3 = 1.5 BLUE = 4 x 0.5 = 2.0 YELLOW = 0.5 x 0.5 = 0.25 Add all products: 12 + 1.5 + 2.0 + 0.25 = 15.75

15. Continue with Scenarios Try to Solve Scenarios 2 and 3 using either the Rectangular Array or Area Model Strategy Day 60, “Multiplying Decimal by Decimal Using Area Model” can be used for more practice problems