Lesson 18 Use Whole Number Facts

- Let’s multiply whole numbers and decimals.

Warm-up True or False: Group Dynamics

Decide if each statement is true or false. Be prepared to explain your reasoning.

$30 \times 2 \times 10 = 6 \times 10$
$30 \times 2 \times 10 = 20 \times 3 \times 10$
$60 \times 10 = 30 \times 20$

Activity 1 Agree or Disagree

Problem 1

Decide whether each equation is true or false and explain or show why.

$4 \times 0.7 = 28$
$5 \times 0.8 = 0.40$
$6 \times 0.03 = (6 \times 3) \times 0.01$
$8 \times 0.07 = (8 \times 7) \times 0.1$

Problem 2

Fill in the blank to make each equation true.

$3 \times 0.7 = 3 \times 7 \times$
$3 \times 0.07 = 3 \times 7 \times$
$5 \times$ $= (5 \times 4) \times 0.1$

Activity 2 Interpret Diagrams and Expressions

Problem 1

Three diagrams. Each squares. Length and width, 1. Each partitioned into 10 rows of 10 of the same size squares. 12 squares shaded in each diagram.

Explain or show how the diagram represents each expression.

$3 \times 0.12$
$(3 \times 12) \times 0.01$
$(3 \times 0.1) + (3 \times 0.02)$

Problem 2

Find the value of $(3 \times 12) \times 0.01$ . Explain or show your reasoning.
Find the value of $(3 \times 0.1) + (3 \times 0.02)$ . Explain or show your reasoning.

Practice Problem

Problem 1

Mai says that $7 \times 0.4$ and $7 \times 0.04$ both have the same value. She says that they are both 28. Do you agree with Mai? Explain or show your reasoning.
Explain why $8 \times 0.03 = (8 \times 3) \times 0.01$ .