# Lesson 10: Multiply!

Let’s get more practice multiplying signed numbers.

## 10.1: Which One Doesn’t Belong: Expressions

Which expression doesn’t belong?

$7.9x$

$7.9\boldcdot (\text- 10)$

$7.9 + x$

$\text-79$

## 10.2: Matching Expressions

Match expressions that are equal to each other.

row 1 row 2 row 3 $(\text-1) \boldcdot 12$ $(\text-64)\boldcdot \frac18$ $1 \boldcdot 15$ $(\text-1) \boldcdot (\text-3) \boldcdot (\text-5)$ $(\text-1) \boldcdot (\text-2) \boldcdot 6$ $(\text-1) \boldcdot (\text-12)$ $1 \boldcdot (\text-3) \boldcdot (\text-5)$ $(\text-\frac{1}{4}) \boldcdot (\text-32)$ $(\text-2) \boldcdot 6$ $(\text-\frac{1}{2}) \boldcdot (\text-16)$ $(\text-3) \boldcdot 5$ $2\boldcdot (\text-4)$ $(\text-\frac12)\boldcdot 16$ $(\text-1) \boldcdot (\text-3) \boldcdot (\text-4)$ $2\boldcdot 4$ $(\text-1) \boldcdot (\text-3) \boldcdot 4$ $(\text-3) \boldcdot (\text-5)$ $1 \boldcdot (\text-15)$

## 10.3: 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
row 1 $790\div 10$  $(7.9)\boldcdot 10$
row 2 $\left(\text- \frac67\right) \boldcdot 7$ $(0.1) \boldcdot (\text- 60)$
row 3 $(2.1) \boldcdot (\text- 2)$ $(\text-8.4) \boldcdot\frac12$
row 4 $(2.5) \boldcdot (\text-3.25)$ $\left(\text{-} \frac52 \right)\boldcdot \frac{13}{4}$
row 5 $(\text-10) \boldcdot (3.2) \boldcdot (\text-7.3)$ $5\boldcdot (\text-1.6) \boldcdot (\text-29.2)$

## Summary

A positive times a positive is always positive. For example, $\frac35 \boldcdot \frac78 = \frac{21}{40}$.

A negative times a negative is also positive. For example, $\text-\frac35 \boldcdot \text-\frac78 = \frac{21}{40}$.

A negative times a positive or a positive times a negative is always negative. For example, $\frac35 \boldcdot \text-\frac78 = \text-\frac35 \boldcdot \frac78 = \text-\frac{21}{40}$.

A negative times a negative times a negative is also negative. For example, $\text-3 \boldcdot \text-4 \boldcdot \text-5 = \text-60$.