Grade: 3, Topic(s): addition/subtraction

## Purpose

To add 12 to any number.

None

Tell children you want them to add 12 to each number they hear. Start by saying a one-digit number or a “friendly” two-digit number, such as 10. Then choose a student to add 12 to *that* sum. Discuss mental math strategies they may be helpful, such as adding 10, and then adding 2 more.

Optional: Make a vertical list, starting with the beginning number and writing each sum below. This visual model is useful in making a clear connection to the mental math.

Part 1, starting with 10 as the starting number, highlights the pattern of adding 10 and then adding 2 more. Part 2 starts with a five and invites children to use the familiar skip-counting pattern of counting by two fives (to add 10) and then add two more. The extension changes the starting number to 7, which requires children will need to think more deeply about the “adding 10 and then adding 2 more” pattern.

Let’s start at 10 and add 12. What number do we have? Now, let’s add 12 again… and then again until we reach at least 100.

- 10, 22, 34, 46, 58, 60, 72, 84, 96, 108…

*If children need more practice or are enjoying their mastery, repeat. If children are ready to move on, move to Part 2.*

Now, let’s start at 5 and add 12. What number do we have? Now, let’s add 12 again…and then again until we reach at least 100.

- 5, 17, 29, 41, 53, 65, 77, 89, 101…

*If children need more practice, repeat. Or, when children seem excited for a new challenge, move to the extension.*

Now, let’s start at 7 and add 12. What number do we have? Now, let’s add 12 again… and then again until we reach at least 100.

- 7, 19, 31, 43, 55, 67, 79, 91, 103…

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