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Math 21 Unit 1 Lesson 1 p. 1 of 3 Math 21 Unit 1 Lesson 1 SWBAT add and subtract integers. 1. Adding and Subtracting Integers Integers: Includes all positive and negative numbers including zero. Using A Number Line: - move to the right when adding a positive number move to the left when adding a negative number Ex. 1. – 4 + (2) = -2 -4 -2 0 start on this number Ex. 2. – 5 + (- 3) = - 8 -8 -5 Without a Number Line: 1. If signs are the same, add the numbers and the answer keeps the same sign. Ex. 3. – 3 + (- 8) = -11 Ex. 4. + 4 + (+ 5) =+9 = 9 Math 21 Unit 1 Lesson 1 p. 2 of 3 2. If signs are different, subtract the numbers (larger number – smaller number). Answer has the same sign as the larger number. Ex. 5. –8 + 11 =3 Ex. 6. 5 + ( -12 ) = -7 Adding and subtracting are opposite operations in math. To subtract, rewrite the question into an addition by adding the opposite. Ex. 7. 5 – 8 = 5 + (-8) = -3 Ex. 8. - 4 - 13 = - 4 + (-13) = -17 Ex. 9. 5 – ( -2) =5+2 =7 Math 21 Unit 1 Lesson 1 p. 3 of 3 Another way to think about Ex. 9 is: two negatives in a row become a positive. Ex. 10. 4 - ( -3) =4+3 =7 If an expression has a variable (letter), apply the above, but carry the variable through. Ex. 11. 5y – 10y = 5y + (-10y) = -5y Exercise 1