Add a 2-digit number and a 1-digit number, missing addend

Teaching Notes

Emphasize using the relationship between addition and subtraction to find the missing addend. Encourage mental math strategies like counting on or subtracting from the sum. Discuss place value alignment.

Vocabulary

Missing addend: The unknown number in an addition problem.

Sum: The total when numbers are added.

Common Mistakes

• Adding the given numbers instead of finding the difference.
• Incorrectly calculating the difference when subtracting to find the missing addend.
• Misunderstanding which number is the sum versus an addend.

Differentiation

Discussion Questions

• How can you use subtraction to help you solve these addition problems?
• What strategy did you use to find the missing number?
• How can you check if your answer is correct?

Extension Activities

• Use fact families.
• Work backward from the sum.
• Use manipulatives.

Parent Tip

Use a number line to find the distance between numbers.

Skill Cluster

Number Sense & Operations

Estimated Time

15 minutes

Skills Practiced

Prerequisites

• Addition facts to 20
• Understanding place value (tens and ones)
• Introduction to inverse operations (addition and subtraction)

Next Steps

• Missing addends with 2-digit + 2-digit numbers
• Missing subtrahends/minuends (subtraction problems)
• Word problems involving missing addends