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Thomas, John Charles N. F. Simeon Voc. H. S.
1. The students will be able to add integers.
2. The students will be able to subtract integers.
3. The students will be able to define:
A. Additive inverse
B. Identity element of addition
C. Associative property of addition
4. The student will be able to follow oral directions.
5. The student will be able to add and subtract integers
without using the adding machine.
6. The students will be able to write a definition for adding
integers and one for subtracting integers.
1. Poster board. (11" x 14")
2. Cut strips of paper from the poster board of a pre-determined
length and width.
3. A ruler or a straightedge.
5. Felt tip pens to write the numerals on the adding machine.
I will tell each class that we are going to make an adding
machine. We will make a machine out of paper. This machine will add
certain combinations of integers. (Note: The extent of the
combinations depends on the length of the scales on the "Addend"
number lines.) Let's get the show on the road. I will give each
student a strip of paper and a ruler. The paper has three lines on
one side. Turn that side face up. We are going to divide each line
into two equal parts. (Note: Give oral instructions as well as visual
instructions for dividing the line into two equal parts.) Ask the
students to put a tick mark," - ", at the midpoint of each line. Tell
students to put a zero besides each tick mark on the lines. (Note:
Turn rulers to the metric side.) Put a tick mark one cm (centimeter)
apart on the line in the middle. Put a tick mark two cm apart for
each of the other two lines. (Note: Check the students' papers for
accuracy.) We are ready to write the numerals on the adding machine.
Count upward using positive integers for each tick mark. Count
downward using negative integers for each tick mark. (Note: Check
papers for errors.)
Now, let's label the lines. Write the word, "SUM," over the line
in the middle. Write the word, "ADDEND," over each of the other two
lines. You have just made an adding machine.
Write "ADDEND + ADDEND = SUM" on the board or overhead projector
to explain adding two integers. Write any combination similar to the
+6 + (+4) = +10
+6 + (-4) = +2
-6 + (+4) = -2
-6 + (-4) = -10
Ask the students to connect the "ADDENDS" with their ruler or
straightedge to verify the answers. (Note: If the same combinations
are used, the students will, hopefully, intuitively determine a
definition for adding or subtracting integers.)
Write "SUM - ADDEND = ADDEND" on the board to explain
subtraction. Write several combinations similar to the one below.
+8 - (+5) = +3
+8 - (-5) = +13
-8 - (+5) = -13
-8 - (-5) = -3
The students can verify the answers by connecting the "SUM" and
the "ADDEND" with a straightedge.
This approach has worked for me in the past.