CCSS.Math.Content.1.NBT.C

Math1st GradeNumber and Operations in Base Ten

Standard Cluster

Use place value understanding and properties of operations to add and subtract.

Common Core State Standards for Mathematics

Cluster contents

CCSS.Math.Content.1.NBT.C is a cluster heading. These are the individual standards under it.

Teacher's field guide

What Students Need to Do: Students break two-digit numbers into tens and ones to add within 100. They find 10 more or 10 less mentally and subtract groups of ten. They use drawings, objects, or equations to show their thinking.
What Mastery Looks Like: Students correctly solve problems such as 36 + 20, 36 + 7, and 70 − 30. They can show tens and ones with blocks, drawings, or equations and explain which place changes.
Common Misconceptions: Students may add or subtract every digit they see without attending to tens and ones. They may think 10 more changes both digits, or count by ones when subtracting whole tens.
How to Assess It: Use an exit ticket with three items: 34 + 20, 47 + 6, and 10 less than 82. Ask students to show one answer with a drawing or equation.

Lesson moves

Give pairs base-ten blocks to build 42, add 30, then add 6 and record each result with an equation.
Ask students to explain in writing why 53 + 20 changes the tens digit but keeps the ones digit the same.
Play a card game where students draw a two-digit number and an operation card showing plus 10, minus 10, or plus 20.
Set up a classroom store where items cost multiples of 10 cents, and students find totals or change using play coins.

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