Accelerated Math 6 August 22, 2013 Adding integers Accelerated Math 6 August 22, 2013

Follow the instructions…  

One Way to Add Integers Is With a Number Line When the number is positive, count to the right. When the number is negative, count to the left.   + 1 2 3 4 5 6 -1 -2 -3 -4 -5 -6

To add a positive integer we move forwards up the number line. Examples We can use a number line to help us add positive and negative integers. –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. Remember: To add a positive integer we move forwards up the number line.

–3 + (–4) = = –7 Examples Remember: -7 -3 Remember: To add a negative integer we move backwards down the number line. 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.   is the same as  

Examples     + -6 -5 -4 -3 -2 -1 1 2 3 4 5 6  

Examples   2 + -6 -5 -4 -3 -2 -1 1 2 3 4 5 6  

Examples       -6 -5 -4 -3 -2 -1 1 2 3 4 5 6  

Examples       -6 -5 -4 -3 -2 -1 1 2 3 4 5 6  

Example 1   2 + -6 -5 -4 -3 -2 -1 1 2 3 4 5 6   Walking 6 steps to the right and then walking 4 back, is the same as starting at 6 and walking 4 to the left.  

Examples                  

Accelerated Math 6 August 22, 2013 Subtracting integers Accelerated Math 6 August 22, 2013

A positive and a negative gives you 0 Example 1     ADD What is left? A positive and a negative gives you 0

Example 2     ADD What is left?

           

Subtract means you change the color Example 7     Subtract What is left? Subtract means you change the color

Subtract means you change the color Example 8     Subtract Subtract means you change the color

Subtract means you change the color Example 9     Subtract Subtract means you change the color

           

    Subtract What do you notice?     ADD

Adding a negative number and subtracting a positive number result in the same value.