Provide pairs of students with two number cubes, buttons, and the red and blue strip of paper from the previous lesson. If these strips are not available, give the students a strip of paper and ask them to color one half of the paper red and the other half blue. Next ask them to count out seven buttons and write that number in purple on a separate sheet of paper. Then ask them to find as many ways as they can to separate the seven buttons into two sets, putting some (or no) buttons on the red side of the paper and some (or no) on the blue side. Ask them to record each way using red and blue numerals to match what they have done. Some of the possible sorts are shown below. There will be five more sorts when the set is complete.
 |
| 7 |
3
5
0 |
4
2
7 |
&Nbsp;
When they have decomposed seven in several ways, help them enter two or three of their findings on a class record chart. Once all their sorts made have been recorded, ask the students whether there are any sorts missing. [There are eight possible sorts of seven objects. Students may need to be reminded to use 0 on each of the sides.]
Call on a volunteer to read one row of the chart. Now demonstrate how to rewrite that entry on the chart as a pair of addition sentences. Then challenge the students to write the same row as a pair of subtraction sentences. [You may wish to model how this is done if the students have not previously encountered the subtraction sign.]
Call on volunteers to read their subtraction sentences aloud. Then write the sum (7) and the four sentences that can be derived from a pair of its addends (say, 5 and 2.) [It will help the students to see the relationships regardless of whether they continue the convention of writing the addends in blue and red and the sum in purple.] Tell the students that this is called a fact family.
The fact family for 7, 5 and 2 is:
5 + 2 = 7
2 + 5 = 7
7 – 5 = 2
7 – 2 = 5
Now ask the students to count out eight buttons on the red side of their strip and repeat the activity, recording all the possible two-addend combinations for eight. [This time there will be nine ways to sort the buttons. You may wish to encourage them to look for a pattern as they make the sets.]
Repeat with other numbers. [The number of ways to sort the buttons will be one more than the number of buttons used. To be sure all the sorts are found, the students might be encouraged to start with all the buttons on one side of the strip, then move them one at a time to the other side of the strip, recording each addend pair as it is displayed.]
Finally, ask the students to choose a number from zero to 10 and write one fact family that has that sum. When the students are ready, ask several volunteers to demonstrate the fact family using buttons and a red and blue strip
of paper. Then ask them to find the addends and sum for that fact family on their Sums to 10 chart.
You may wish to ask the students to select two addends and their sum to record for their portfolio by drawing a picture illustrating that fact family.
