Grade 1Adding and Subtracting within 201.OA.A.2

Adding Three Numbers

Look for a pair that makes 10 or a double first.

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You can add in any order and make a ten. Adding three numbers uses both.

$4 + 3 + 6$: 4 and 6 make 10, then 3 more is 13.

Key idea

With three numbers, look for two that make 10, or a double. Add those first.
  • Pairs that make 10: 1 and 9, 2 and 8, 3 and 7, 4 and 6, 5 and 5.
  • Doubles: 2 and 2, 3 and 3, 4 and 4 …
  • If you find neither, add the first two, then the third.

Why it works

You can add in any order and group the numbers any way you like. The total stays the same.

Worked example: Find the ten

What is $7 + 2 + 3$?
  1. 7 and 3 make 10.
  2. $10 + 2 = 12$

Answer: 12

Worked example: Find a double

What is $5 + 4 + 5$?
  1. $5 + 5 = 10$.
  2. $10 + 4 = 14$

Answer: 14

For grown-ups: Roll three dice and add. Ask, “Which two did you add first? Why?”

Practice

Pass with 3 right answers, the last 2 in a row. Each right answer earns 2 XP.

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Builds on

Leads to

This is one of the top rungs of Grade 1.

Sources and further reading

  • Common Core State Standards for Mathematics, Grade 1, 1.OA.A.2: solve word problems that add three whole numbers with a sum up to 20
  • Institute of Education Sciences practice guide: Assisting Students Struggling with Mathematics: Intervention in the Elementary Grades (WWC 2021006)
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