Download U1 1.1 Lesson 1

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