Have students look at the flash cards for Groups 1 and 2. Ask them to first remove all the cards with a ten in the problem.
- Sort the cards into pairs so that the two cards have problems that belong to the same fact family. (13 − 9 with 13 − 4, 15 − 9 with 15 − 6, 14 − 9 with 14 − 5, 16 − 9 with 16 − 7. There will be three cards without pairs: 12 − 9, 17 − 9, 11 − 9.)
- What strategies did you use to make the pairs? For example, why did you pair 13 − 9 and 13 − 4? (Possible response: The two problems have the same numbers: 4, 9, and 13.)
- What are the addition number sentences that go with 13 − 9 and 13 − 4? (4 + 9 = 13 and 9 + 4 = 13.)
Repeat the last two questions until all four pairs are discussed.
