🎓 Grade 1📄 Free PDF✅ Answer Keys🎯 4 Classroom Sets

Addition Facts within 20 · Free Worksheets (Grade 1)

Practice addition facts within 20 (Grade 1) with free printable PDF worksheets. 4 pre-packaged classroom sets with 100% verified step-by-step answer keys, plus an unlimited live customizer for teachers and homeschoolers.

📐Aligned to Common Core (CCSS.MATH.CONTENT.1.OA.C.6)·5-10 min per sheet

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PanMaths.comAddition Facts within 20 Worksheets • Set A (Standard)

Name: __________________________

Date: _____________ Period: ____

Score: _____ / 10

1+11

Workspace:

12+1

Workspace:

5+6

Workspace:

1+12

Workspace:

15+2

Workspace:

3+1

Workspace:

6+5

Workspace:

6+13

Workspace:

2+7

Workspace:

10.

13+7

Workspace:

PanMaths.com • Free Printable Math WorksheetsPage 1 of 2

PanMaths.comAnswer Key & Worked Solutions • Set A (Standard)

Answer Key

Total Problems: 10

1+11= 12

1. Add Ones: 1 + 1 = 2 ➔ Write 2

2. Add Tens: 0 + 1 = 1 ➔ Write 1

Total Sum: 1 + 11 = 12 ✅

12+1= 13

1. Add Ones: 2 + 1 = 3 ➔ Write 3

2. Add Tens: 1 + 0 = 1 ➔ Write 1

Total Sum: 12 + 1 = 13 ✅

5+6= 11

1. Core Addition Fact: 5 + 6 = 11

2. Make-a-Ten Strategy: 5 + 5 + 1 = 10 + 1 = 11

3. Total Sum: 11 ✅

1+12= 13

1. Add Ones: 1 + 2 = 3 ➔ Write 3

2. Add Tens: 0 + 1 = 1 ➔ Write 1

Total Sum: 1 + 12 = 13 ✅

15+2= 17

1. Add Ones: 5 + 2 = 7 ➔ Write 7

2. Add Tens: 1 + 0 = 1 ➔ Write 1

Total Sum: 15 + 2 = 17 ✅

3+1= 4

1. Core Addition Fact: 3 + 1 = 4

3. Total Sum: 4 ✅

6+5= 11

1. Core Addition Fact: 6 + 5 = 11

2. Make-a-Ten Strategy: 6 + 4 + 1 = 10 + 1 = 11

3. Total Sum: 11 ✅

6+13= 19

1. Add Ones: 6 + 3 = 9 ➔ Write 9

2. Add Tens: 0 + 1 = 1 ➔ Write 1

Total Sum: 6 + 13 = 19 ✅

2+7= 9

1. Core Addition Fact: 2 + 7 = 9

3. Total Sum: 9 ✅

10.

13+7= 20

1. Add Ones: 3 + 7 = 10 ➔ Write 0, Carry 1 to Tens

2. Add Tens: 1 (carry) + 1 + 0 = 2 ➔ Write 2

Total Sum: 13 + 7 = 20 ✅

PanMaths.com • Answer Key & SolutionsPage 2 of 2

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Worksheet Info

Categorygrade-1

Grade LevelGrade 1

DifficultyEasy, Medium, Hard, Sprint

Time5-10 min

CCSS CodeCCSS.MATH.CONTENT.1.OA.C.6

Skills Practiced

✓ Addition Facts within 20

Key Strategies

🔟 Make a Ten Strategy: When solving 8 + 5: Break 5 into 2 and 3. Add 8 + 2 to make 10, then add the remaining 3 to get 13!
⚡ Doubles Plus One: If you know 6 + 6 = 12, then 6 + 7 is just 1 more: 13!
🔢 Count On by 1, 2, or 3: For small addends (like 14 + 3), count forward directly: 15, 16, 17.

🎮 Interactive Warm-Up

Addition Mastery

Warm up with 60 seconds of rapid mental math practice before printing!

Play Speed Game Free →

Related Worksheets

📄 Counting Objects (1–20)View →📄 Number Line Hops (Within 20)View →📄 Number Bonds to 10View →📄 Number Bonds to 20View →

📜 Standard: CCSS.MATH.CONTENT.1.OA.C.6🔗 CCSS.MATH.CONTENT.1.OA.B.3🔗 CCSS.MATH.CONTENT.1.OA.A.1

Mastering Addition Facts within 20: Core Concepts & Mental Models

Addition within 20 bridges single-digit math into base-ten thinking. First graders move from counting on their fingers to powerful mental strategies like 'Make a Ten' and 'Doubles Plus One', establishing computational speed for multi-digit math.

Worked Example & SolutionTeacher Step-by-Step Method

📝 Problem: Solve: 8 + 7 = ?

Worked Solution: 1. Make a ten: 8 needs 2 to make 10. 2. Decompose 7 into 2 + 5. 3. Add: (8 + 2) + 5 = 10 + 5 = 15.

💡 Essential Strategies for Addition Facts within 20

🔟 Make a Ten Strategy

When solving 8 + 5: Break 5 into 2 and 3. Add 8 + 2 to make 10, then add the remaining 3 to get 13!

⚡ Doubles Plus One

If you know 6 + 6 = 12, then 6 + 7 is just 1 more: 13!

🔢 Count On by 1, 2, or 3

For small addends (like 14 + 3), count forward directly: 15, 16, 17.

⚠️ Common Mistakes & Teacher Fixes

⚠️Losing track when counting on large numbers

Why students stumble: Counting 8 hops from 7 on fingers leads to off-by-one errors (saying 14 instead of 15).

Teacher Fix: Use the Make-a-Ten strategy: 7 + 3 = 10, plus 5 is 15!

Example: 7 + 8 = 15, not 14.

📖 Key Mathematical Vocabulary

Bridge 10

A mental math technique where you complete 10 first before adding the rest of the second number.

Doubles Fact

An addition fact where a number is added to itself (e.g. 7 + 7 = 14).

Near Doubles

Numbers that are 1 apart, solved using doubles (e.g. 7 + 8 = 7 + 7 + 1 = 15).

🎯 4 Differentiated Classroom Sets Included

Standard 10Version A

Set A: Core Facts to 20 (10 Problems)

Addition facts with sums from 11 to 20 requiring bridging ten.

Anti-CheatVersion B

Set B: Alternate Numbers (10 Problems)

Identical structure with alternate number combinations to prevent desk-copying.

ChallengingVersion C

Set C: Mixed Facts Within 20 (8 Problems)

Mixed addition combinations within 20 combining near-doubles and making ten.

Speed SprintVersion D

Set D: 3-Minute Fluency Sprint (15 Problems)

15 rapid addition problems to evaluate speed, automaticity, and accuracy.

❓ Frequently Asked Questions

How do you solve a addition facts within 20 problem step by step?

Here is a worked example: "Solve: 8 + 7 = ?". Solution: 1. Make a ten: 8 needs 2 to make 10. 2. Decompose 7 into 2 + 5. 3. Add: (8 + 2) + 5 = 10 + 5 = 15.

What is the core learning objective for addition facts within 20?

Add within 20, demonstrating fluency for addition within 10 and using strategies such as making ten and decomposing numbers to bridge 10. This directly aligns with Common Core Standard CCSS.MATH.CONTENT.1.OA.C.6.

What is the most common mistake students make with addition facts within 20?

A frequent pitfall is: "Losing track when counting on large numbers". Why students stumble: Counting 8 hops from 7 on fingers leads to off-by-one errors (saying 14 instead of 15). How to fix it: Use the Make-a-Ten strategy: 7 + 3 = 10, plus 5 is 15! (Example: 7 + 8 = 15, not 14.)

What is included in the 4 differentiated worksheet sets?

Set A covers standard core practice (Addition facts with sums from 11 to 20 requiring bridging ten.). Set B is an Anti-Cheat version with alternate numbers to prevent copying. Set C features challenging problems, and Set D is a timed sprint.

Are these addition facts within 20 worksheets free to print with answer keys?

Yes! Every single worksheet on PanMaths is 100% free with no sign-up needed. Each sheet includes a dedicated Answer Key on Page 2 with step-by-step intermediate evaluation lines for 1-minute grading.