Lesson 10Multiply!

Learning Goal

Let’s get more practice multiplying signed numbers.

Learning Targets

I can solve problems that involve multiplying rational numbers.

Warm Up: Which One Doesn’t Belong: Expressions

Which expression doesn’t belong?

$7.9 x$
$7.9 + x$
$7.9 \cdot (- 10)$
$- 79$

Activity 1: Matching Expressions

Your teacher will give you cards with multiplication expressions on them. Match the expressions that are equal to each other. There will be 3 cards in each group.

$(- 1) \cdot 12$	$(- 64) \cdot \frac{1}{8}$	$1 \cdot 15$
$(- 1) \cdot (- 3) \cdot (- 5)$	$(- 1) \cdot (- 2) \cdot 6$	$(- 1) \cdot (- 12)$
$1 \cdot (- 3) \cdot (- 5)$	$(- \frac{1}{4}) \cdot (- 32)$	$(- 2) \cdot 6$
$(- \frac{1}{2}) \cdot (- 16)$	$(- 3) \cdot 5$	$2 \cdot (- 4)$
$(- \frac{1}{2}) \cdot 16$	$(- 1) \cdot (- 3) \cdot (- 4)$	$2 \cdot 4$
$(- 1) \cdot (- 3) \cdot 4$	$(- 3) \cdot (- 5)$	$1 \cdot (- 15)$

Activity 2: Row Game: Multiplying Rational Numbers

Evaluate the expressions in one of the columns. Your partner will work on the other column. Check in with your partner after you finish each row. Your answers in each row should be the same. If your answers aren’t the same, work together to find the error.

column A	column B
$790 \div 10$	$(7.9) \cdot 10$
$(- \frac{6}{7}) \cdot 7$	$(0.1) \cdot (- 60)$
$(2.1) \cdot (- 2)$	$(- 8.4) \cdot \frac{1}{2}$
$(2.5) \cdot (- 3.25)$	$(- \frac{5}{2}) \cdot \frac{13}{4}$
$(- 10) \cdot (3.2) \cdot (- 7.3)$	$5 \cdot (- 1.6) \cdot (- 29.2)$

Are you ready for more?

A sequence of rational numbers is made by starting with 1, and from then on, each term is one more than the reciprocal of the previous term. Evaluate the first few expressions in the sequence. Can you find any patterns? Find the 10th term in this sequence.

$1 1 + \frac{1}{1} 1 + \frac{1}{1 + 1} 1 + \frac{1}{1 + \frac{1}{1 + 1}} 1 + \frac{1}{1 + \frac{1}{1 + \frac{1}{1 + 1}}} \dots$

Lesson Summary

A positive times a positive is always positive. For example, $\frac{3}{5} \cdot \frac{7}{8} = \frac{21}{40}$ .

A negative times a negative is also positive. For example, $(- \frac{3}{5}) \cdot (- \frac{7}{8}) = \frac{21}{40}$ .

A negative times a positive or a positive times a negative is always negative. For example, $\frac{3}{5} \cdot (- \frac{7}{8}) = (- \frac{3}{5}) \cdot \frac{7}{8} = (- \frac{21}{40})$ .

A negative times a negative times a negative is also negative. For example, $(- 3) \cdot (- 4) \cdot (- 5) = (- 60)$ .

Lesson 10Multiply!

Learning Goal

Learning Targets

Warm Up: Which One Doesn’t Belong: Expressions

Problem 1

Activity 1: Matching Expressions

Problem 1

Activity 2: Row Game: Multiplying Rational Numbers

Problem 1

Are you ready for more?

Problem 1

Lesson Summary