Warm up: p. 349
# 65 ­ 70
OBJECTIVES:
•solve inequalities by multiplying or dividing by a positive number
•solve inequalities by multiplying or dividing by a negative number
Section 7­5
_____________________
When you multiply or divide each side of an inequality by the same positive number, the inequality remains the same.
2 < 6
3 > ­9
4(2) < (6)4
3 > ­9 3 3
8 < 24
1 > ­3
1
Example 1: Solve.
a. 8x < 40
b. d > 7
2
Example 2: Lana earns $8 per hour in the summer working at the zoo. Which inequality can be used to find how many hours she must work in a week to earn at least $120?
A. 8x < 120
B. 8x < 120
C. 8x > 120
D. 8x > 120
2
When you multiply or divide each side of an inequality by the same negative number, the inequality symbol must be reversed for the inequality to remain true.
7 > 1
­4 < 16
­2(7) > (1)­2
­4 < 16
­4 ­4
­14 < ­2
1 > ­4
Example 3: Solve each inequality and graph the solution on a number line.
a. x < 4
­2
­10
­9
­8 ­7
­6
­5 ­4
­3
­2
­1
0
1
2
3
4
5
6
7
8
9
10
b. ­7x > ­56 ­10
­9
­8 ­7
­6
­5 ­4
­3
­2
­1
0
1
2
3
4
5
6
7
8
9
10
3
Guided Practice:
1. List the steps you would use to solve y < 6.
­12
2. Find the Error. Ben and Troy each solved ­45 > 9k. Who is
correct? Explain.
Ben
Troy
­45 > 9k
­45 > 9k
­45 > 9k
9 9
­45 > 9k
9 9
­5 < k
­5 > k
Solve each inequality.
3. 2x < 8
5. ­4t > ­20
4. 3x > ­6
6. a > 10
5
4
Solve and graph each inequality.
7. ­8 > k ­0.4
­10
­9
­8
­7
­6
­5 ­4
­3
­2
­1
0
1
2
3
4
5
6
7
8
9
10
8. m < 1.2
­7
­10
­9
­8
­7
­6
­5 ­4
­3
­2
­1
0
1
2
3
4
5
6
7
8
9
10
9. ­5s < ­3.5
­10
­9
­8
­7
­6
­5 ­4
­3
­2
­1
0
1
2
3
4
5
6
7
8
9
10
10. Julia delivers pizzas on weekends. Her average tip is $1.50 for each pizza she delivers. How many pizzas must she deliver to earn at least $20 in tips?
5
Do you have any Vocab questions?
OBJECTIVES:
HOMEWORK: p. 353 ­ 354
# 14 ­ 38 even
&
p. 354
"Practice Quiz 2"
6