Add Three Numbers Within 20 | 1st Grade Math

Add Three Numbers Within 20 - Grade 1 Math
Grade 1 Math  ›  Addition & Subtraction  ›  Lesson 15
Grade 1 Math - Addition and Subtraction

Add Three Numbers Within 20

Learn how to add three numbers, or three addends, when the total is 20 or less. Students use make-10 pairs, doubles, known facts, and flexible grouping to find easier sums.

When adding three numbers, look for two addends that are easy to combine first. You can change the order of the addends or choose which two to combine first, and the sum stays the same.

Add three numbers Three addends Make 10 Addition within 20 1st Grade Math

๐ŸŽฏ What You Will Learn

Add three numbers with totals within 20
Combine three addends accurately and keep track of the total.
Look for a pair that makes 10
Making 10 first often turns a three-number sum into an easier fact.
Use doubles and known facts
Helpful pairs such as 5 + 5 or 6 + 6 can make the work quicker.
Choose a helpful order
Add the easiest pair first, then add the remaining number.
For parents & teachers — standards alignment: CCSS 1.OA.A.2 calls for Grade 1 students to solve word problems involving the addition of three whole numbers with sums of 20 or less. This lesson also supports CCSS 1.OA.B.3 by using properties of addition as strategies and CCSS 1.OA.C.6 by applying efficient addition strategies within 20. Students do not need to use formal property names. Texas TEKS 1.3(C), 1.3(D), and 1.3(E) reinforce composing 10 with two or more addends, applying basic-fact strategies within 20, and explaining addition strategies.

๐Ÿง  Key Vocabulary

addend — a number being added.
sum — the result of adding two or more numbers.
total — the amount altogether.
make 10 — combine two addends that have a sum of 10.
double — a fact with the same addend twice, such as 6 + 6.
strategy — a helpful way to solve a problem.

➕ What Does Adding Three Numbers Mean?

An addition equation can have more than two addends. In 2 + 6 + 4, all three numbers are parts of one total. Because this expression uses only addition, you can choose any two addends to combine first, then add the third.

2 + 6 + 4 = 12
Big idea: when an expression uses only addition, you can choose any two addends to combine first. Look for a pair that makes 10, a double, or another easy known fact.

๐Ÿ”Ÿ Make 10 First

Making 10 is especially useful when adding three numbers. Look for two addends that combine to make 10.

6 + 4 = 10
→
10 + 2
=
12

So 2 + 6 + 4 = 12. The 6 and 4 were the most helpful pair to add first.

๐Ÿ› ️ Four Useful Strategies

Make 10 Look for two addends that make 10.
Use a double Put matching addends together first.
Use a known fact Begin with a pair you already know quickly.
Add in steps Add two numbers, keep the subtotal, then add the third.
Common mistake: do not forget the third addend. If you solve 7 + 3 + 5, stopping at 7 + 3 = 10 is not enough. You must still add 5, so the total is 15.

๐ŸŒŸ 25 Worked Examples

Try each problem first. Then open “Show solution” to compare your strategy.
1 Add in order
Find the sum: 2 + 3 + 4 = □.
Show solution Hide solution

Add the first two numbers: 2 + 3 = 5. Then add 4: 5 + 4 = 9. So 2 + 3 + 4 = 9.

2 Build a total step by step
Find the sum: 5 + 2 + 3 = □.
Show solution Hide solution

First, 5 + 2 = 7. Then 7 + 3 = 10. So the sum is 10.

3 Make 10 first
Find the sum: 6 + 4 + 2 = □.
Show solution Hide solution

Look for a pair that makes 10. Since 6 + 4 = 10, add those first. Then 10 + 2 = 12. So the sum is 12.

4 Make 10 with non-neighboring addends
Find the sum: 7 + 2 + 3 = □.
Show solution Hide solution

The 7 and 3 make 10. Add them first: 7 + 3 = 10. Then 10 + 2 = 12. So the sum is 12.

5 Choose the helpful pair
Find the sum: 8 + 1 + 2 = □.
Show solution Hide solution

The 8 and 2 make 10. Add them first: 8 + 2 = 10. Then 10 + 1 = 11. So the sum is 11.

6 Use 9 + 1
Find the sum: 9 + 4 + 1 = □.
Show solution Hide solution

The 9 and 1 make 10. Add them first: 9 + 1 = 10. Then 10 + 4 = 14. So the sum is 14.

7 Use a double
Find the sum: 4 + 4 + 3 = □.
Show solution Hide solution

Use the known double 4 + 4 = 8. Then 8 + 3 = 11. So the sum is 11.

8 Put the matching addends together
Find the sum: 6 + 2 + 6 = □.
Show solution Hide solution

The two 6s make a known double: 6 + 6 = 12. Then 12 + 2 = 14. So the sum is 14.

9 Use a known fact first
Find the sum: 5 + 6 + 2 = □.
Show solution Hide solution

Start with a fact you know: 5 + 6 = 11. Then 11 + 2 = 13. So the sum is 13.

10 Make 5, then add
Find the sum: 2 + 3 + 7 = □.
Show solution Hide solution

The first two addends make 5: 2 + 3 = 5. Then 5 + 7 = 12. So the sum is 12.

11 Make 10 before adding the last number
Find the sum: 3 + 7 + 6 = □.
Show solution Hide solution

The 3 and 7 make 10. Then 10 + 6 = 16. So the sum is 16.

12 Change the order to make it easier
Find the sum: 2 + 8 + 5 = □.
Show solution Hide solution

You can add the 2 and 8 first because they make 10. Then 10 + 5 = 15. So the sum is 15.

13 Three equal addends
Find the sum: 5 + 5 + 5 = □.
Show solution Hide solution

Start with the double: 5 + 5 = 10. Then 10 + 5 = 15. So the sum is 15.

14 Adding zero
Find the sum: 0 + 7 + 8 = □.
Show solution Hide solution

Adding 0 does not change a number. So 0 + 7 + 8 has the same total as 7 + 8. Since 7 + 8 = 15, the sum is 15.

15 Make 10 with 9 and 1
Find the sum: 6 + 1 + 9 = □.
Show solution Hide solution

The 1 and 9 make 10. Add them first: 1 + 9 = 10. Then 10 + 6 = 16. So the sum is 16.

16 Reach a total of 20
Find the sum: 8 + 2 + 10 = □.
Show solution Hide solution

The 8 and 2 make 10. Then 10 + 10 = 20. So the sum is 20.

17 Use a double to make 20
Find the sum: 7 + 6 + 7 = □.
Show solution Hide solution

Put the two 7s together: 7 + 7 = 14. Then 14 + 6 = 20. So the sum is 20.

18 Create an easier known sum
Find the sum: 9 + 3 + 6 = □.
Show solution Hide solution

The 3 and 6 make 9. Then 9 + 9 = 18. So the sum is 18.

19 Make 10, then add 7
Find the sum: 4 + 6 + 7 = □.
Show solution Hide solution

The 4 and 6 make 10. Then 10 + 7 = 17. So the sum is 17.

20 Choose a convenient first pair
Find the sum: 2 + 5 + 8 = □.
Show solution Hide solution

The 2 and 8 make 10. Add them first: 2 + 8 = 10. Then 10 + 5 = 15. So the sum is 15.

21 Three groups in a story
There are 4 red counters, 6 blue counters, and 3 green counters. How many counters are there altogether? 4 + 6 + 3 = □.
Show solution Hide solution

The 4 and 6 make 10. Then 10 + 3 = 13. There are 13 counters altogether.

22 Use a double in a story
A basket has 5 apples, 5 pears, and 7 oranges. How many pieces of fruit are there altogether? 5 + 5 + 7 = □.
Show solution Hide solution

Use the double 5 + 5 = 10. Then 10 + 7 = 17. There are 17 pieces of fruit.

23 Make 10 in a story
There are 8 birds on one branch, 2 on another branch, and 6 on the ground. How many birds are there in all? 8 + 2 + 6 = □.
Show solution Hide solution

The 8 and 2 make 10. Then 10 + 6 = 16. There are 16 birds in all.

24 Explain the best first pair
Find the sum: 8 + 5 + 2 = □. Which two addends would you add first?
Show solution Hide solution

Add 8 and 2 first because they make 10. Then 10 + 5 = 15. So the sum is 15.

25 Show two ways
Find the sum: 4 + 6 + 5 = □. Show two possible ways to begin.
Show solution Hide solution

One way is 4 + 6 = 10, then 10 + 5 = 15. Another way is 6 + 5 = 11, then 11 + 4 = 15. Both give the same sum: 15.

๐ŸŽฎ Independent Practice — 30 Problems

  1. Find the sum: 2 + 4 + 3 = □.
  2. Find the sum: 5 + 1 + 4 = □.
  3. Find the sum: 7 + 3 + 2 = □.
  4. Find the sum: 6 + 2 + 4 = □.
  5. Find the sum: 8 + 2 + 5 = □.
  6. Find the sum: 9 + 1 + 6 = □.
  7. Find the sum: 4 + 4 + 5 = □.
  8. Find the sum: 6 + 6 + 3 = □.
  9. Find the sum: 3 + 7 + 8 = □.
  10. Find the sum: 5 + 5 + 9 = □.
  11. Find the sum: 2 + 8 + 7 = □.
  12. Find the sum: 1 + 9 + 9 = □.
  13. Find the sum: 4 + 6 + 6 = □.
  14. Find the sum: 7 + 2 + 7 = □.
  15. Find the sum: 3 + 5 + 8 = □.
  16. Find the sum: 10 + 2 + 6 = □.
  17. Find the sum: 0 + 9 + 4 = □.
  18. Find the sum: 5 + 3 + 5 = □.
  19. Find the sum: 8 + 4 + 6 = □.
  20. Find the sum: 7 + 5 + 4 = □.
  21. Find the sum: 6 + 4 + 7 = □.
  22. Find the sum: 8 + 3 + 2 = □.
  23. Find the sum: 9 + 5 + 1 = □.
  24. Find the sum: 4 + 8 + 2 = □.
  25. There are 4 red counters, 3 blue counters, and 5 green counters. How many counters are there altogether? Write and solve an addition equation.
  26. There are 6 birds in a tree, 4 on a fence, and 7 on the ground. How many birds are there in all?
  27. A bowl has 8 apples, 2 pears, and 5 oranges. How many pieces of fruit are there altogether?
  28. In 8 + 5 + 2, which two addends would you add first to make 10? Then find the total.
  29. Solve 6 + 7 + 4. Name a helpful pair to add first.
  30. Write an addition equation with three addends whose sum is 18.

๐Ÿ† Lesson Test — 15 Questions

  1. Find the sum: 1 + 3 + 5 = □.
  2. Find the sum: 2 + 3 + 6 = □.
  3. Find the sum: 1 + 2 + 9 = □.
  4. Find the sum: 4 + 4 + 2 = □.
  5. Find the sum: 3 + 5 + 7 = □.
  6. Find the sum: 5 + 5 + 8 = □.
  7. Find the sum: 4 + 6 + 9 = □.
  8. Find the sum: 10 + 3 + 5 = □.
  9. Find the sum: 0 + 6 + 9 = □.
  10. Find the sum: 3 + 7 + 10 = □.
  11. There are 2 red cubes, 4 blue cubes, and 7 yellow cubes. How many cubes are there altogether?
  12. A desk has 4 crayons, 5 pencils, and 8 markers. How many school supplies are there in all?
  13. In 1 + 8 + 9, which two addends can make 10 first? Then find the total.
  14. Solve 4 + 5 + 5. Name one helpful strategy.
  15. Solve 9 + 2 + 8. Show one useful first pair and give the total.

๐Ÿ” Complete Answer Key

Show practice answer key Hide practice answer key

Practice Answers

1. 9
2. 10
3. 12
4. 12
5. 15
6. 16
7. 13
8. 15
9. 18
10. 19
11. 17
12. 19
13. 16
14. 16
15. 16
16. 18
17. 13
18. 13
19. 18
20. 16
21. 17
22. 13
23. 15
24. 14
25. 12 counters; for example, 4 + 3 + 5 = 12.
26. 17 birds; 6 + 4 + 7 = 17.
27. 15 pieces of fruit; 8 + 2 + 5 = 15.
28. Add 8 and 2 first; 8 + 2 = 10, then 10 + 5 = 15.
29. 17. A helpful first pair is 6 and 4 because 6 + 4 = 10.
30. Possible answer: 5 + 6 + 7 = 18.
Show test answer key Hide test answer key

Test Answers

1. 9
2. 11
3. 12
4. 10
5. 15
6. 18
7. 19
8. 18
9. 15
10. 20
11. 13 cubes; 2 + 4 + 7 = 13.
12. 17 school supplies; 4 + 5 + 8 = 17.
13. Add 1 and 9 first; 1 + 9 = 10, then 10 + 8 = 18.
14. 14. One helpful strategy is to add the two 5s first: 5 + 5 = 10, then 10 + 4 = 14.
15. 19. One useful first pair is 2 and 8: 2 + 8 = 10, then 10 + 9 = 19.

๐Ÿ’ก Common Mistakes to Watch For

Stopping after two addends
A three-addend equation is not finished until all three numbers have been included.
Missing an easy make-10 pair
In 8 + 5 + 2, adding 8 + 2 first makes the problem much easier.
Thinking the order changes the total
You can choose a different pair to add first and still get the same sum.
Losing track of the subtotal
After adding two numbers, say or write that subtotal before adding the last number.
What comes next: Lesson 16 applies addition and subtraction within 20 to a wider range of word problems, including different problem situations and unknown positions.

๐Ÿ”— Related Lessons

Lesson 8 — Number Bonds & Ways to Make 10 Review combinations that make 10 before using them with three addends. Lesson 9 — Addition Strategies Within 20 Review make-10, doubles, and other strategies for addition within 20.

๐Ÿ–จ️ Printable Companion

A future Add Three Numbers Within 20 Practice Pack can include three-addend equations, make-10 puzzles, doubles practice, three-group picture problems, mixed strategy practice, and a complete answer key.

← Lesson 14: Missing Numbers & Unknowns Grade 1 Math Hub Next: Addition & Subtraction Word Problems Within 20

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