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October 5, 2009
Math 102
Objective: Students will learn how to subtract
integers.
Aim: How does adding the opposite mean the
same as subtraction, and how does finding the
absolute value of numbers help us when adding
and subtracting integers?
NYS Mathematics Standards: 7.N.12
Prior Knowledge: Find each opposite:
+7____
-5____
+6 _____
Which number has the greater absolute value?
-4 or 1____ 10 or -16____ 9 or -9_____
Mini-lesson:
The first step in subtracting integers is to
rewrite the subtraction expression as an
addition expression.
2 – 5 can be written as the addition expression 2 + (-5)
When we ADD a negative, we go to the LEFT
2 - 5 = -3 is the same as 2 + (-5) = -3
Group Practice:
(Mr. Brooks will hand out red and yellow counters)
Find the difference of 2 and 5. Use counters.
1. Write the subtraction expression 2 – 5.
2. To subtract integers, add the opposite. Write the addition
expression 2 + (-5). This is the new expression.
3. Use 2 positive (yellow) counters to represent the first
number.
4. Use 5 negative (red) counters to represent the second
number.
5. You can make 2 zero pairs (1 red and 1 yellow cancel
each other out).
6. There are 3 negative counters left.
7. Write the difference. 2 + (-5) = -3
Guided Practice:
State which of the following are correct or are not correct and explain
why they are wrong:
1.
-12 – (-2) = -10 ____________
2.
The difference of -17 and 6 is -11 ________
3.
|-11| has a greater absolute value than |5|
___________________
Independent Practice:
Complete Exercises 13, 16, 20, 21, 24 and 28
Homework: “Homework Practice” worksheet
on integer subtraction