In this Grade 8 lesson from Yoshiwara Core Math, Chapter 7, students learn how to subtract signed numbers by converting subtraction problems into equivalent addition problems using the rule that subtracting a positive number equals adding its negative counterpart, and subtracting a negative number equals adding a positive. Using number line models, students practice computing differences such as (-3) - (+5) and 2 - (-5) to build fluency with signed number operations. The lesson covers key vocabulary including sum and difference and develops the foundational subtraction rule that applies to all integers.
Section 1
📘 Subtracting Signed Numbers
This lesson reveals a key shortcut: any subtraction problem can be transformed into an addition problem. By changing the sign of the number being subtracted, you can use the addition rules you already know to find the answer.
Coming up, you'll explore this concept on number lines and work through interactive examples. Soon, you'll be solving practice problems to master this new skill.
Section 2
Subtracting a Positive Number
Subtracting a positive number is the same as adding the corresponding negative number. For both operations, we move to the left on the number line.
Think of subtracting a positive number as taking away value. This makes you move left on the number line, which is exactly what happens when you add a negative number. It's two ways of describing the same decrease.
Section 3
Subtracting a Negative Number
Subtracting a negative number gives the same result as adding a positive number. For both operations, we move to the right on the number line.
Imagine someone cancels a debt you owe. Taking away that negative debt increases your net worth! Similarly, subtracting a negative number is like adding a positive one, causing you to move right on the number line.
Section 4
Subtraction Rule for Signed Numbers
To subtract a signed number, we can convert the problem into an equivalent addition problem.
To rewrite a subtraction problem, leave the first number alone, change the sign of the second number, and change the subtraction symbol to an addition symbol.
Why learn new rules for subtraction? We don't have to! This rule lets us turn any subtraction problem into an addition problem. Just add the opposite of the number being subtracted, and use the addition rules you already know.
Section 5
Interpreting Notation
When we see a string of numbers separated by plus or minus signs, we’ll treat it as a sum of signed numbers.
An expression like is easier to solve if you read it as a sum of signed numbers: . This way, you can add them in any order and avoid confusion with subtraction.
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Section 1
📘 Subtracting Signed Numbers
This lesson reveals a key shortcut: any subtraction problem can be transformed into an addition problem. By changing the sign of the number being subtracted, you can use the addition rules you already know to find the answer.
Coming up, you'll explore this concept on number lines and work through interactive examples. Soon, you'll be solving practice problems to master this new skill.
Section 2
Subtracting a Positive Number
Subtracting a positive number is the same as adding the corresponding negative number. For both operations, we move to the left on the number line.
Think of subtracting a positive number as taking away value. This makes you move left on the number line, which is exactly what happens when you add a negative number. It's two ways of describing the same decrease.
Section 3
Subtracting a Negative Number
Subtracting a negative number gives the same result as adding a positive number. For both operations, we move to the right on the number line.
Imagine someone cancels a debt you owe. Taking away that negative debt increases your net worth! Similarly, subtracting a negative number is like adding a positive one, causing you to move right on the number line.
Section 4
Subtraction Rule for Signed Numbers
To subtract a signed number, we can convert the problem into an equivalent addition problem.
To rewrite a subtraction problem, leave the first number alone, change the sign of the second number, and change the subtraction symbol to an addition symbol.
Why learn new rules for subtraction? We don't have to! This rule lets us turn any subtraction problem into an addition problem. Just add the opposite of the number being subtracted, and use the addition rules you already know.
Section 5
Interpreting Notation
When we see a string of numbers separated by plus or minus signs, we’ll treat it as a sum of signed numbers.
An expression like is easier to solve if you read it as a sum of signed numbers: . This way, you can add them in any order and avoid confusion with subtraction.
Book overview
Jump across lessons in the current chapter without opening the full course modal.
Continue this chapter