To review the concept of subtraction, read *Ten Sly Piranhas*. Ask the children to act out with counters what is happening in the story and to write the related subtraction sentence for each page. Then call out a sum and have each child show you a domino with that many spots. Encourage the students to write the addition equation suggested by the domino.

In the example above, students may suggest the following addition equation:

**6 + 4 = 10**

Next, choose two dominoes with the same number of total spots, then display them with one crossed over the other so that both parts of the upper domino but only one part of the bottom domino is visible. Now tell the children that both dominoes have the same number of spots and that they are to guess how many spots are covered on the bottom domino. When a correct response is given, display the domino and ask the students to explain how they knew.

Model the activity a few more times, being sure to include one example of what happens when one domino has 0 spots on one side. Then place the students in pairs and have them take turns being the teacher. This activity will help them focus on the relationship of subtraction to addition. Finally, ask the pairs to sort the set of Double 6 dominoes by the sums that the dominoes represent. Ask the students to write a sentence about this exercise for their portfolios.

Now call the children together and ask a volunteer to choose a domino that is not a double and write the four number sentences (two addition and two subtraction) that the domino suggests. You may wish to repeat this exercise with other volunteers.

For the domino above, the following addition and subtraction sentences are suggested:

4 + 5 = 9

5 + 4 = 9

9 - 5 = 4

9 - 4 = 5

As the lesson concludes, remind the students that they need to practice the addition facts and that making more triangle-shaped flash cards will help them to do so.

### Reference

- Wise, William.
*Ten Sly Piranhas*. New York: Dial, 1993.