Lesson 13 Mentally Add and Subtract Tens

    • Let’s add and subtract tens in our heads.

Warm-up Number Talk: Add and Subtract 10

Find the value of each expression mentally.

Activity 1 Introduce Write Numbers: Numbers to 99 by 10

We are going to learn a new way to do the Write Numbers center.

Activity 2 Add and Subtract 10

Problem 1

Find the number that makes each equation true. Then tell what you notice.

  5. Talk to your partner. What patterns do you notice?

    I notice that when I add 10,

    I notice that when I subtract 10,

Problem 2

Find the number that makes each equation true. After each set of equations, tell what pattern you notice.

  1. I notice that

  2. I notice that

  3. I notice that

Practice Problem

Problem 1

Find the value of each expression.

  5. What patterns do you notice?