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Plus and Minus in a Row

Part of the Numbers & Operations section of Coddy's Pre-Algebra journey. Lesson 22 of 57.

When two signs meet, merge them into one. Two of the same sign make a plus; two different signs make a minus. So $8 - \left(-3\right)$ is $8+3$ , which is 11, while $8 + \left(-3\right)$ is $8-3$ , which is 5.

Why? A minus sign means 'the opposite of'. One minus flips the direction of a move, and a second minus flips it back. In $8 + \left(-3\right)$ there is only one flip, so the move goes left. In $8 - \left(-3\right)$ there are two, so it goes right.

Merging first turns every problem into one you already know. $-8 - \left(-3\right)$ becomes $-8+3$ : different signs, so subtract the sizes and keep the sign of -8. The answer is -5.

Challenge

Work out $2 - \left(-5\right)$ and $-4 - \left(-1\right)$ , then mark both answers on the number line.

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Numbers & Operations

2Mental Math

Friendly Pairs Take Away the Total Recap: Mental Math

5Subtracting Integers

Add the Opposite Subtracting a NegativePlus and Minus in a RowDistance Between Numbers Recap: Subtracting Integers

8Square Roots

Perfect Squares Undoing a Square Roots in Expressions The Root Sign Groups Between Two Whole Numbers Recap: Square Roots

11Final Challenges

Final: Every Rule at Once Final: Roots and Powers Final: The Freezer Final: Over the Bar Final: On the Line

3Negative Numbers

Below Zero Opposites Greater or Less Absolute Value Recap: The Number Line

6Multiplying and Dividing

Negative Times Positive Two Negatives Counting the Negatives Dividing Integers Zero in Division Recap: Multiply and Divide

9Putting It All Together

Powers Before Products Negatives Inside Negative Bases in Sums Everything at Once Recap: The Full Order