Subtracting Integers with Counters How to subtract integers

Subtracting Integers with Counters

How to subtract integers with counters 1. Rewrite the problem – Keep the first number the same – Change the problem from subtraction to addition – Make the last number its opposite 2. Lay out your counters to represent the problem. 3. Get rid of zero pairs 4. Count up what you have

Here’s how you rewrite the problem! -8 – 7 -8 + -7 -8 stays the same 7 changes to its opposite -7 Subtraction becomes addition Additive Inverse Two integers that are opposite of each other are additive inverses. The sum of any number and its additive inverse is zero.

5 - -6 5 + +6 Now rewrite the problem. 5 positive units + 6 positive units Get rid of pairs. What do you have left? 11 positive units Answer = 11

-10 - -3 Now rewrite the problem. -10 + +3 10 negative units + 3 positive units Get rid of pairs. What do you have left? 7 negative units Answer = -7

5 - 13 Now rewrite the problem. 5 + -13 5 positive units + 13 negative units Get rid of pairs. What do you have left? 8 negative units Answer = -8

You try & rewrite these problems Rewritten Problems 1. -4 – 8 = 1. -4 + -8 = 2. 9 – 17 = 2. 9 + -17 = 3. 3 - -5 = 3. 3+5= 4. 6 – 10 = 4. 6 + -10 = 5. -8 - - 17 = 5. -8 + 17 = Now follow adding rules or use algebra tiles to solve! 1. -12 2. -8 3. 8 4. -4 5. 9

Solve these practice problems! 1. 2. 3. 4. 5. 6. 7. 8. -5 - -4 = 4 - -7 = -12 – 4 = 9 - -5 = -5 - -9 = -10 – 8 = -4 - -4 = -12 -3 = 1. 2. 3. 4. 5. 6. 7. 8. -1 11 -16 14 4 -18 0 -15

Word Problems 1. A submarine is situated at 450 feet below sea level and sinks 75 feet. What is the new position of the submarine? -450 – 75 = -525 feet The new position of the submarine was 525 feet below sea level. 2. The temperature at 8 pm was 6°F. At 2 am the temperature decreased 13 degrees. What was the temperature at 2 am? 6 – 13 = -7°F The temperature at 2 am was -7°F.