Читать книгу Basic Math & Pre-Algebra All-in-One For Dummies (+ Chapter Quizzes Online) - Mark Zegarelli - Страница 60

The last rule you need to know is how to subtract a negative number. For example, suppose you want to calculate . Here’s the up and down rule:

Subtracting a negative number is the same as adding a positive number — go up on the number line.

This rule tells you that is the same as , so start at :

When subtracting negative numbers, you can think of the two negative signs canceling each other out to create a positive.

Q. Use the number line to add .

A. 2. On the number line, means which brings you to 2:

Q. Use the number line to add .

A. 4. On the number line, means start at 6, down 2, which brings you to 4:

Q. Use the number line to add .

A. −7. On the number line, means which brings you to −7:

Q.

A. 16. Switch around the two numbers with the signs attached:

Now you can drop the plus sign and use the negative sign for subtraction:

Q. Use the number line to subtract

A. −5. On the number line, means start at −1, down 4, which brings you to −5:

Q. Use the number line to subtract .

A. −2. The expression means start at (because the two negative signs cancel each other out), which brings you to :

5 Use the number line to solve the following addition problems:

(a)

(b)

(c)

(d)

(e)

(f)

6 Solve the following addition problems without using the number line:

(a)

(b)

(c)

(d)

(e)

(f)

7 Use the number line to solve the following subtraction problems:

(a)

(b)

(c)

(d)

(e)

(f)

8 Solve the following subtraction problems without using the number line:

(a)

(b)

(c)

(d)

(e)

(f)