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Basic Subtraction

Overview

If you have 5 apples...

What is it?

Taking a smaller number away from a larger one to find the difference.

History

Ancient merchants used subtraction tokens to calculate profit and loss.

Key Idea

Think: 'How far apart are these two numbers on the number line?'

Practice This Topic

Concept Guide

Plain English: Subtraction is finding the distance. If you are on Step 10 and you want to go back to Step 2, subtraction tells you how many steps to walk.

Real-world example: Battery Life. You have 80% and use 15%. How much is left?

How to do it

  1. Write the big number on top.
  2. Write the small number on bottom (line up the right side!).
  3. Start at the ones column (far right).
  4. Top minus Bottom equals Answer.
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Common Pitfall

Swapping the order! 10 - 2 is easy. 2 - 10 is a totally different beast (negative numbers).

Word Problem
"A gamer has 100 HP. They take 15 damage from a slime. How much health is left?"
Reasoning: 100 - 15 = 85 HP.

Practice Examples

Vertical
9 - 4 --- 5
Standard setup.