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

## Purpose

To add 9 to any number.

None

Choose a number (preferably less than 6) for children. Then add 9 to that number and say the number sentence aloud. For example, you might say “Four plus nine equals thirteen.” Choose a child to add 9 to *that* sum.

Children should use the method for adding 9 they feel most comfortable with, such as adding 10 and subtracting 1, or adding 5 and then adding 4 more. Repeat this activity with other starting numbers (perhaps greater than 6, but less than 10) as time allows.

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 has children start with 0 and then add 9. Part 2 moves to having children start at 1, prompting them to notice that each result in this “chain” will be one more each time. The extension uses starting numbers that are greater than 3, but less than 10 (e.g., 5).

Let’s start at 0 and add 9. What number do we have? Now, let’s add 9 again…and then again until we reach at least 100.

- 0, 9, 18, 27, 36, 45, 54, 63, 72, 81, 90, 99, 108

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

Let’s start at 1 and add 9. What number do we have? Now, let’s add 9 again…and then again until we reach at least 100.

- 1, 10, 19, 28, 37, 46, 55, 64, 73, 82, 91, 100, 109

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

Let’s start at 5 (or any number greater than 3, but less than 10) and add 9. What number do we have? Now, let’s add 9 again…and then again until we reach at least 100.

Example:

5, 14, 23, 32, 41, 50, 59, 68, 77, 86, 95, 104

This work is licensed under a

Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.