# Lesson: Subtract Integers Using Models (Counters/Numberline)

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### Lesson Objective

Subtract integers using counters and models

### Lesson Plan

 Standard ·         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 Aim/Objective: Key Points 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) Assessment: 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   Closing ·         Exit Ticket ·         Describe to your neighbor – how do you subtract with a number line?  Switch – how do you subtract with counters     ·

### Lesson Resources

 Notes Subtract Integers with Models   Notes 2,712 Notes 6 Subtract With Models 1,488 Notes 6 Subtract With Models 1,018 Exit Ticket Subtract Integers models 1,161