1. Skill Check
Lesson Presentation
Lesson Quiz

2. Skill Check
1. 47 – 18 = 29
2. 65 – 48 = 17
– 88 = 15

3. Earth Science Kick-’em-Jenny is an underwater volcano in the Caribbean Sea.
Eruptions have caused the volcano to grow. In 1962, the summit elevation of Kick-’em-Jenny was –235 meters. In 2002, the summit elevation was –182 meters. By how many meters did the elevation of the volcano change? You will use integer subtraction to answer this question.

4. Subtracting Integers Words To subtract an integer, add its opposite.
Numbers
3 – 7 = 3 + (–7) = –4
Algebra
a – b = a + (–b)

5. 1 4 – 10 = 4 + (–10) = –6 Subtracting Integers
EXAMPLE 1
Subtracting Integers
4 – 10 =
4 + (–10)
To subtract 10, add its opposite, –10.
= –6
Add 4 and –10.

6. 1 4 – 10 = 4 + (–10) = –6 –2 – (–9) = –2 + 9 = 7 Subtracting Integers
EXAMPLE 1
Subtracting Integers
4 – 10 =
4 + (–10)
To subtract 10, add its opposite, –10.
= –6
Add 4 and –10.
–2 – (–9) =
–2 + 9
To subtract –9, add its opposite, 9.
= 7
Add –2 and 9.

7. 2 Evaluate the expression when x = –9. x – (–40) x – (–40) =
EXAMPLE 2
Evaluating Variable Expressions
Evaluate the expression when x = –9.
x – (–40)
SOLUTION
x – (–40) =
–9 – (–40)
Substitute –9 for x.
= –9 + 40
To subtract –40, add 40.
= 31
Add –9 and 40.

8. 2 Evaluate the expression when x = –9. 7 – x 7 – x = 7 – (–9) = 7 + 9
EXAMPLE 2
Evaluating Variable Expressions
Evaluate the expression when x = –9.
7 – x
SOLUTION
7 – x =
7 – (–9)
Substitute –9 for x.
= 7 + 9
To subtract –9, add 9.
= 16
Add 7 and 9.

9. Evaluating Change You can use subtraction to find the change in a variable quantity such as elevation or temperature. Subtract the original value of the quantity from the value after the change.

10. 3 = –182 – (–235) = –182 + 235 = 53 Evaluating Change
EXAMPLE 3
Evaluating Change
By how many meters did the elevation of the volcano Kick-’em-Jenny change if the elevation in 1962 was –235 meters and –182 meters in 2002? To answer this question, you can subtract the elevation in 1962 from the elevation in Write a verbal model.
Change in
elevation =
Elevation in
2002 –
1962
= –182 – (–235)
Substitute values.
= –
To subtract –235, add 235.
= 53
Add –182 and 235.
The difference is 53, so the summit elevation of Kick-’em-Jenny increased by 53 meters from 1962 to 2002.
ANSWER

11. Lesson Quiz
Find the difference.
1. 15 – 19 –4
2. –8 – 7
–15
3. –11 – (–20) 9
Evaluate the expression when t = –10.
4. 22 – t 32
5. 7 – t – 26 –9
6. Challenge If a is a positive integer and b is a negative integer, is the value of the expression a – b a positive integer or a negative integer? Explain.
Positive; when changed to the sum of a and the opposite of b, the result is the sum of two positive integers whose sum will be positive.