Subtraction Fundamentals Summary

Arithmetic · Axiom Academy

SUMMARY Subtraction Fundamentals Summary Key takeaways from Unit 3 — what subtraction means, the strategies that crack it, and how it ties back to addition. Subtraction is the opposite of addition — what you add, you can subtract. Order matters — 8 - 3 is not the same as 3 - 8 . Fact families connect operations — knowing 3 + 5 = 8 helps you know 8 - 5 = 3 . Multiple strategies work — count back, count up, or think addition. Core Concept What Subtraction Is Subtraction means "taking away." Start from one number, remove an amount, and see what's left. The answer is called the difference The starting number is the minuend The amount taken away is the subtrahend Start at the bigger number and count backwards by the amount you're subtracting. Count backwards the amount you're subtracting Works well for small subtrahends Track the count on a number line Turn a subtraction into a missing-addend addition. Instead of taking away, ask what you'd add to get back to the start. Addition facts help with subtraction Three related numbers make four facts — and those four facts show how + and - are connected. 2 addition facts + 2 subtraction facts From a Fact Family to Four Facts Example Recap: Solving 15 - 8 by Thinking Addition We want the difference 15 - 8 . Rewrite it as a missing addend: 8 + ? = 15 . Ask "8 plus what equals 15?" — the answer is 7 . So 15 - 8 = 7 , found using an addition fact instead of counting back.

This is the written version of the interactive lesson above. See the full Arithmetic course.