Integer: Addition and Subtraction Ask volunteers to come to the board to show a solution for each calculation. Tell them that each example must include at least one negative integer card. Discuss all possible solutions for each calculation and ask pupils to tell you any patterns or relationships that they notice.

Integer - Addition and Subtraction Ask volunteers to come to the board to show a solution for each calculation. Tell them that each example must include at least one negative integer card. Discuss all possible solutions for each calculation and ask pupils to tell you any patterns or relationships that they notice. Fill in the blanks.

–2 + 5 = = 3 You can model integer addition with a number line. ADDING INTEGERS You can model integer addition with a number line. –2 + 5 = = 3 -2 3 How can we use the number line to work out –2 + 5? Start at –2 (click to highlight the –2 on the number line) and count forwards 5. On a number line we move to the right for forwards (in a positive direction) and to the left for backwards (in a negative direction). Explain that the answer can be positive or negative depending on the starting point. It is important to stress this fact because when pupils learn the rules for multiplying and dividing negative numbers they often confuse these rules for the rules for addition and subtraction. Start at zero. Go to first addend. Move in the direction and distance of the second addend.

–3 + –4 = = –7 ADDING INTEGERS Here’s another example: -7 -3 How can we use the number line to work out –3 + -4? Explain that when we add a negative number we have to move backwards down the number line. The answer can be positive or negative depending on the starting point. Stress that adding a negative number is equivalent to subtracting the positive value of that number. Start at zero. Go to first addend. Move in the direction and distance of the second addend.

KEY POINTS… ADDING INTEGERS When adding a positive integer, move to the right on the number line. When adding a negative integer, move to the left on the number line. Start at zero. Move the direction and distance of the 1st addend Move the direction and distance of the 2nd addend.

ADDING INTEGERS Try these: -8 + -7 = -9 + 4 -10 + 6 + -2 4 + -3 + 6 + -5

5 – 8 = = –3 You can use a number line to model SUBTRACTING INTEGERS You can use a number line to model subtraction of integers too. 5 – 8 = = –3 -3 5 How can we use the number line to work out 5 – 8? Start at 5 (click to make the 5 orange) and count backwards 8.

–4 – (–7) = = 3 –4 – (–7) is the same as –4 + 7 SUBTRACTING INTEGERS -4 3 Here is another example of subtracting a negative number. Again, explain carefully that subtracting a negative number is equivalent to adding. In this example, –4 is the starting point and then we move 7 forwards up the number line. Ask pupils to tell you the equivalent calculation before revealing it on the board. –4 – (–7) is the same as –4 + 7

KEY IDEA Since the inverse of subtraction is addition, every subtraction problem can be made into an addition problem. For example: -1 – 2 = -1 + (-2) Prove this using a number line.

Try the following: 4 – (−2) = 1 – 6 = −9 – (−5) = −10 + −7 – 4

Reflection: 1) What general rules can we develop for adding integers? 2) What general rules can we develop for subtracting integers?

Adding and Subtracting Integers Practice Choices: White Board work (teacher-led) Tic-Tac-Toe (word problems) Buzz Math