1. Solving Inequalities by Adding or Subtracting
Holt Algebra 1
Warm Up
Lesson Presentation
Lesson Quiz
Holt McDougal Algebra 1

2. Warm Up Graph each inequality. Write an inequality for each situation.
1. The temperature must be at least –10°F.
2. The temperature must be no more than 90°F.
–10 10
x ≥ –10
x ≤ 90
–90 90
Solve each equation.
3. x – 4 = 10 14
4. 15 = x + 1.1
13.9

3. Objectives Solve one-step inequalities by using addition.
Solve one-step inequalities by using subtraction.

4. Solving one-step inequalities is much like solving one-step equations
Solving one-step inequalities is much like solving one-step equations. To solve an inequality, you need to isolate the variable using the properties of inequality and inverse operations.

6. Helpful Hint
Use an inverse operation to “undo” the operation in an inequality. If the inequality contains addition, use subtraction to undo the addition.

7. Solve each inequality and graph the solutions.
Check It Out! Example 1
Solve each inequality and graph the solutions.
a. s + 1 ≤ 10
Since 1 is added to s, subtract 1 from both sides to undo the addition.
s + 1 ≤ 10
–1 –1 9
–10 –8 –6 –4 –2 2 4 6 8 10
s + 0 ≤ 9
s ≤ 9
b > –3 + t
Since –3 is added to t, add 3 to both sides to undo the addition.
> –3 + t +3
> 0 + t
–10 –8 –6 –4 –2 2 4 6 8 10
t <

8. Solve the inequality and graph the solutions.
Check It Out! Example 1c
Solve the inequality and graph the solutions.
q – 3.5 < 7.5
Since 3.5 is subtracted from q, add 3.5 to both sides to undo the subtraction.
q – 3.5 < 7.5
q – 0 < 11
q < 11 –7 –5 –3 –1 1 3 5 7 9 11 13

9. Since there can be an infinite number of solutions to an inequality, it is not possible to check all the solutions. You can check the endpoint and the direction of the inequality symbol.
The solutions of x + 9 < 15 are given by x < 6.

10. Check It Out! Example 2
The Recommended Daily Allowance (RDA) of iron for a female in Sarah’s age group (14-18 years) is 15 mg per day. Sarah has consumed 11 mg of iron today. Write and solve an inequality to show how many more milligrams of iron Sarah can consume without exceeding RDA.

11. Check It Out! Example 2 Continued
Understand the problem 1
The answer will be an inequality and a graph that show all the possible amounts of iron that Sarah can consume to reach the RDA.
List important information:
• The RDA of iron for Sarah is 15 mg.
• So far today she has consumed 11 mg.

12. Check It Out! Example 2 Continued
Make a Plan
Write an inequality.
Let x represent the amount of iron Sarah needs to consume.
Amount taken
plus
15 mg
is at most
amount needed 11 + x  15
11 + x  15

13. Check It Out! Example 2 Continued
Solve 3
11 + x  15
Since 11 is added to x, subtract 11 from both sides to undo the addition.
– –11
x  4
Draw a solid circle at 4. 1 2 3 4 5 6 7 8 9 10
Shade all numbers less than 4.
x  4. Sarah can consume 4 mg or less of iron without exceeding the RDA.

14. Check It Out! Example 2 Continued
Look Back 4
Check
Check a number less than 4. 
 15
 15
14  15
Check the endpoint, 4. 
11 + x = 15
Sarah can consume 4 mg or less of iron without exceeding the RDA.

15. Let p represent the number of additional pounds Josh needs to lift.
Check It Out! Example 3
What if…? Josh wants to try to break the school bench press record of 282 pounds. He currently can bench press 250 pounds. Write and solve an inequality to determine how many more pounds Josh needs to lift to break the school record. Check your answer.
Let p represent the number of additional pounds Josh needs to lift.
250 pounds
plus
additional pounds
is greater than
282 pounds.
250 + p
>
282

16. Check It Out! Example 3 Continued
– –250
p > 32
Since 250 is added to p, subtract 250 from both sides to undo the addition.
Check
Check the endpoint, 32.
Check a number greater than 32.
p = 282 
p > 282
> 282
283 > 282 
Josh must lift more than 32 additional pounds to reach his goal.

17. Lesson Quiz: Part I
Solve each inequality and graph the solutions.
1. 13 < x + 7
x > 6
2. –6 + h ≥ 15
h ≥ 21
y ≤ –2.1
y ≤ –8.8

18. Lesson Quiz: Part II
4. A certain restaurant has room for 120 customers. On one night, there are 72 customers dining. Write and solve an inequality to show how many more people can eat at the restaurant.
x + 72 ≤ 120; x ≤ 48, where x is a natural number