Model Multiplying
Two Decimals
Name
Chapter 9, Lesson 3A
Objective: To use an array model to multiply decimals by decimals
Multiply 0.4 ! 0.8.
You need to find 0.4 of a group of 0.8.
Think
1 ! __
1 " ___
1 and __
1 " 0.1
You know that __
10
10
100
10
8.
4 of a group of __
Find __
10
10
So, 0.1 ! 0.1 " 0.01.
The product of 0.4 and 0.8 will be in the hundredths.
8440-W_G5_CH09L03A_TA_01b
To find the product, model
each factor on one
10 ! 10 grid which shows hundredths.
1 Shade 8 of the columns to show 0.8.
Shade 4 of the rows to show 0.4.
0.4
8440-W_G5_CH09L03A_TA_01c
0.8
2 The 32 squares where the shading
overlaps shows the product, 0.4 ! 0.8.
0.4
Copyright © by William H. Sadlier, Inc. All rights reserved.
So, 0.4 ! 0.8 " 0.32.
8 " ___
32
4 ! __
Check: __
10
10
100
0.8
32 " 0.32
___
100
Practice8440-W_G5_CH09L03A_TA_01e_anno
Multiply. Use each 10 ! 10 grid to model 8440-W_G5_CH09L03A_TA_01f_anno
each product.
_G5_CH09L03A_TA_01d_anno
1. 0.7 ! 0.3
2. 0.5 ! 0.8
3. 0.6 ! 0.6
Discuss and Write
4. What do you notice about the relationship between the factors and
the product when multiplying two decimals less than 1?
Grade 5, Lesson 9-3A
5105-9_WB05_211 211
211
2/11/13 9:31 AM
Model Multiplying
Two Decimals
Name
Chapter 9, Lesson 3A
Practice
_CH09L03A_TA_02a_anno
8440-W_G5_CH09L03A_TA_02b_anno
Multiply. Use each 10 ! 10 grid to model each
product.
8440-W_G5_CH09L03A_TA_02c_anno
5. 0.3 ! 0.9
6. 0.7 ! 0.6
7. 0.9 ! 0.4
Multiply. Use a separate sheet of paper to model each product.
8.
0.8
9.
0.4
10.
0.3
! 0.9
! 0.7
! 0.6
11.
0.4
! 0.6
12.
15.
0.7
! 0.5
0.2
! 0.2
13.
0.9
! 0.7
14.
0.5
! 0.3
Solve. Use a strategy that works best for you. Show your work.
16. An artist designs a rectangular logo that
17. An average cat has a body that is about
is 0.8 meter by 0.3 meter. She reduces it
0.5 meter long. The average tail is about
so that the sides are 0.2 times as large.
0.6 times as long as the body. What is the
What are the new dimensions?
length of the tail of an average cat?
18. A recipe for fruit cobbler calls for
0.3 kilogram of apples and 0.8 kilogram
of pears. A chef wants to make 0.8 times
as much. How many kilograms of fruit
will he use in all?
19. Emmett has a 1-kilogram bag of potatoes.
He composted 0.2 kilogram of the potatoes
because they were soft. The amount he
cooked was 0.7 of what was left. How
many kilograms did Emmett cook?
Copyright © by William H. Sadlier, Inc. All rights reserved.
Problem Solving
Test Preparation
20. When Jake multiplied 0.7 times another number, his answer was 0.49.
a. Explain how to find the other factor.
b. What numbers did Jake multiply?
212 Grade 5, Lesson 9-3A
5105-9_WB05_212 212
For additional Practice, go to page 254 in this Workbook.
Then go to Lesson 9-4, pages 300–301 in the Student Book.
2/11/13 9:31 AM