K-5 friendly lesson

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Complete the Subtraction Sentence - Up to 20

❓ Two types of missing numbers! In subtraction, finding the missing number changes depending on WHERE the missing number is. Let's learn the rules.

Lesson 6

Concept

Missing numbers in subtraction are tricky because there are two different rules! 🎯 **Rule 1: The Missing WHOLE (The First Number)** **___ - 6 = 10** If the FIRST number is missing, that is the biggest number in the sentence. It's the "Whole" number! To find the big number, you have to **ADD** the two parts together. * 10 + 6 = 16. * So, **16** - 6 = 10. 🎯 **Rule 2: The Missing PART (The Middle Number)** **18 - ___ = 12** If the MIDDLE number is missing, you already have the big number (18), and you have a small part (12). To find the other small part, you just **SUBTRACT** the part you know from the big number! * 18 - 12 = 6. * So, 18 - **6** = 12.

Try it

Pay attention to where the blank is! **Instructions:** Does the blank come first (Add) or second (Subtract)? **Problem 1: ___ - 5 = 11** * The first number is missing! We need the BIG number. Add them! * 11 + 5 = ___ * Answer: ___ **Problem 2: 17 - ___ = 9** * The middle number is missing. We need a small part. Subtract! * 17 - 9 = ___ * Answer: ___ **Problem 3: 15 - ___ = 10** * Answer: ___ **Problem 4: ___ - 8 = 12** * Answer: ___