Lesson: Subtract Integers Using Models (Counters/Numberline)
· 6NSO.C9 Know integer subtraction is the inverse of integer addition; use the number line to model addition and subtraction of integers and add and subtract integers
Subtract integers using counters and models
· To subtract a positive number on the number line, move left
· To subtract a negative number on the number line, move right
· A negative and positive unit together equal one (a black counter and white counter together equal one)
Directions: Use counters or a number line to solve the following subtraction problems.
1. 8 – –7
2. 3 – 9
3. -7 – (–9)
The number line below shows the number sentence: -4 + 6 = 2 Write a subtraction number sentence for the same number line.
Warm Up: (5 mins)
· Review addition of positive and negative integers
§ 16 + -8
§ -1 + 7
§ 3 + 8
§ 4 + -10
§ -5 + -9
§ -2 + 9
Opening: (5 mins)
· Today we are going to explore subtract with positive and negative integers
· Usually when we think of subtraction, we think about taking away
· Today when we think of subtraction, I want us to add thinking about doing the opposite of addition.
· We can use this line of thinking because subtraction and addition are inverse operations – they are the opposite of one another.
Intro/Direct Instruction: (10 mins)
· Model with students using the number line to subtract integers
· Tell students that the first number tells us where to start on the number. The operation and the second number tell us what direction to go in.
· Walk through an example --- when adding -2 to a number we would move 2 units to the left -- however since we are subtracting negative 2 we need to move two units to the right
· Explain that when we subtract a positive we move the LEFT
· When we subtract a negative we move the RIGHT
· Walk students through using counters to subtract. Remind them that subtraction in some cases is a way to describe taking away. Show a model with two positive numbers (9 – 5) in this case you are taking away five from nine
· However, sometimes it is not this easy. Let’s look at the following example:
· Otis earned $5 babysitting. He owes Latoya $7.
· To set up this problem, we will start with the 5 dollars Otis has – we represent that with 5 white counters. Now we need to take away $7 or 7 white tiles. However, we only have the five white counters so it’s not possible to take away 7. In order for us to take away 7 white counters, we need to add 2 more white counters. In order to add the two white counters we have to add 2 black counters. We can do this because a white counter and a black counter together equal 0. Now we can take away seven white counters and we are left with two black counters – meaning our final answer is two black counters or two negatives (-2)
Guided Practice: (10mins)
· Allow students to practice with number lines and with counter examples – walking them through each step?
· For number line problems:
o Ask: where do we start
o Which way are we going to move?
o How many spaces are we going to move?
· For counters:
o What does my starting board look like? (How many counters, what color)
o How many are we taking away?
o Do we have enough? (Yes – take them away and solve; No – next question)
o How many more do I need in order to take that amount away?
o What counters do I need to add to the board (you have to add the same number of white as black or vice versa)
Independent Practice: (15 mins)
· Students complete worksheet – teacher circulates to monitor understanding/practice – or pull a small group of students who struggled during the guided practice
· Exit Ticket
· Describe to your neighbor – how do you subtract with a number line? Switch – how do you subtract with counters
|Notes Subtract Integers with Models Notes||
|Notes 6 Subtract With Models||
|Notes 6 Subtract With Models||
|Exit Ticket Subtract Integers models||