To review the concept of subtraction, name two sections of the food pyramid (vegetables, fruits, meats, cereal and grains, and milk and dairy products). Place the students in pairs and assign one student in each pair to locate three
to five pictures of food belonging to the fruit section.
Ask the other student to find three to five pictures of meat. Now ask the pairs to discuss the number of food pictures that they collected all together and to compare the number of pictures each student collected. Call on a
volunteer pair to describe the compilation and the comparison of their pictures in words and in addition and subtraction sentences. Repeat with other pairs. Then name a difference, such as two, and have each pair model the meaning of the subtraction sentence by combining all their pictures and making two new sets of food pictures. Call on several groups to explain how they constructed sets with
the given difference. Repeat, if you wish, with other differences.
Using six food pictures in one group and one food picture in another group, ask the students to dictate a set of related addition and subtraction sentences that describe the joining and comparison of these groups.
The sentences for these groups will be:
7 – 1 = 6
7 – 6 = 1
6 + 1 = 7
1 + 6 = 7
Ask the students whether the order of the addends changes the sum. [It does not.] Then ask whether the order of the numbers matters in a subtraction sentence. [It does matter. Subtraction is not a commutative operation.]
Next, have the students make two groups of food pictures of any size that they choose as long as the sum of the groups is 12 or less. Then ask them to generate addition and subtraction sentences that can be modeled using the
pictures in their groups. If the students seem comfortable with this procedure, encourage them to make other pairs of picture groups with a sum of their choice and then combine and compare the groups, writing equations to describe each
action. This activity is designed to help them focus on the commutative property and on the relation of subtraction to addition. When all the students are ready, suggest that they make a set of seven pictures and a set of zero
pictures and write the four related addition and subtraction sentences, as shown below:
7 – 7 = 0
0 + 7 = 7
7 – 0 = 7
7 + 0 = 7
Then call the students together and ask a volunteer to make two sets. Call on a second student to write the two addition sentences, and ask a third volunteer to write the two subtraction sentences that the food picture groups suggest. You may wish to repeat this procedure with other trios of volunteers. Finally, invite one of the students to make two sets of food pictures, each containing three pictures. Call on a volunteer to write the related addition and subtraction sentences that use these sets. [These will be: 3 – 3 = 0 and 3 + 3 = 6.]
Finally, ask them to draw two of the groups that they made during this lesson and write number sentences that describe the combination and comparison of the groups. You may wish to add these recordings to their portfolios. These provide evidence of their growth in understanding of the important topics central to this lesson.
