Addition: Add Whole Tens - Missing Number (427)

Teaching Notes

Encourage students to use mental math strategies and place value understanding to find the missing addend. Relate the problem to known facts and the inverse relationship of addition and subtraction.

Vocabulary

Missing Addend: A number in an addition problem that is unknown.

Whole Tens: Numbers like 10, 20, 30, etc.

Common Mistakes

• Confusing the operation, e.g., adding instead of subtracting.
• Errors in basic subtraction facts when performing the inverse operation.
• Incorrectly applying place value strategies, especially when 'crossing' tens is implicitly involved.

Differentiation

Discussion Questions

• How does knowing your addition facts help you solve for a missing number?
• What strategy did you use to find the missing number in the equation?
• Can you explain why subtracting helps solve for the missing addend?
• How is this problem like adding two-digit numbers, and how is it different?

Extension Activities

• Use a number line to find missing addends.
• Create your own missing number problems.
• Work with larger whole tens.

Parent Tip

Give your child a total and one number, ask them to find the missing number.

Skill Cluster

Number Sense and Operations

Estimated Time

15 minutes

Skills Practiced

Prerequisites

• Adding multiples of ten to 2-digit numbers
• Subtracting multiples of ten from 2-digit numbers
• Missing addends within 20

Next Steps

• Missing addends with any 2-digit number
• Addition and subtraction of multiples of 100
• Addition: Add Whole Tens - Missing Number - Set B
• Addition: Add 2-digit Numbers - Missing Addend
• Subtraction: Subtract Whole Tens - Missing Number