Grades Grade 1 Operations & Algebraic ThinkingFinding the Missing Number

Finding the Missing Number

➕ Operations & Algebraic Thinking

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Finding the Missing Number

Some equations have a mystery number — use what you know to find it!

Sometimes a number in an equation is hidden, like 8 + ? = 11. Your job is to play detective and find the missing value. Think: "What number do I need to add to 8 to get 11?"

🔎Solving 8 + ? = 11

We know: 8 + ? = 11

Strategy 1 — Count on from 8: 9, 10, 11. We counted up 3.
→ The missing number is 3!

Check: 8 + 3 = 11 ✅

🧩Solving ? + 6 = 13

We know: ? + 6 = 13

Think: what + 6 = 13?
Count back from 13: 13 − 6 = 7
→ The missing number is 7!

Check: 7 + 6 = 13 ✅

Strategies for missing numbers:

1Count on: start at the known number and count up to the total

2Count back: subtract the known number from the total

3Use a fact you know: if 5 + 5 = 10, then 5 + ? = 10 → ? = 5

4Always check your answer by plugging it back into the equation!

✏️ Try It!

What is the missing number? 6 + __ = 15

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Remember This!

Use a related subtraction fact! If 6 + __ = 15, then 15 − 6 = __ gives you the answer. Addition and subtraction are best friends!

Take Quiz 📝 — 25 Questions