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↩️ How Addition Undoes Subtraction

Addition and subtraction undo each other. Learn to use that connection to check your answers and crack missing-number problems.

lessons

~15 min

to learn

🔢 Math

subject

Ages 6–12

level

Start the course →

What you’ll learn

Opposites That UndoUnderstand that addition and subtraction are inverse operations that undo each other.Addition and subtraction are opposites: adding and then subtracting the same number cancels out. Because they undo each other, they share the same three numbers, so 15 + 7 = 22 also gives 22 - 7 = 15.
Check and SolveUse the inverse relationship to check calculations and solve missing-number problems.Because subtraction undoes addition, you can check 15 + 7 = 22 by computing 22 - 7 = 15. The same idea solves puzzles: for ? + 9 = 14, undo the +9 with 14 - 9 = 5. Undoing makes your math trustworthy.

Questions this course answers

You start at 8, add 5, then subtract 5. Where do you end up?

Adding and subtracting the same number cancel, so you return to 8.

To check that 15 + 7 = 22, you can calculate...

Undo the addition: 22 - 7 should return 15.

Grounded in trusted sources

Khan Academy Kids
PBS Kids — early math
National Council of Teachers of Mathematics (NCTM)

Every Wunder lesson is built from real, reputable sources — never invented.

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➖Inequalities on a Number Line 🍽️Listing All the Possibilities 🧠Mental Math for Adding and Subtracting 🧠Mental Math with Large Numbers 🧩Missing Numbers and Grouping in Addition 🧮Multi-Step Addition and Subtraction Problems 🏙️Multi-Step Problems with Large Numbers 🔢Number Patterns and Sequences

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