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| 12 Theory slides |
| 9 Exercises - Grade E - A |
| Each lesson is meant to take 1-2 classroom sessions |
Here are a few recommended readings before getting started with this lesson.
Kevin loves to go fishing with his father. They usually fish on a nearby lake. At the lake, small fishing boats are rented to groups of tourists for daily fishing trips.
For safety reasons, each boat can carry at most 600 pounds of weight. Additionally, each boat can hold a maximum of five people.
An inequality, like an equation, is a mathematical statement that compares two quantities. An inequality contains the symbols <, >, ≤, or ≥. There are several ways each inequality can be phrased.
Inequality Symbol | Key Phrases |
---|---|
< | & ∙ is less than & ∙ is fewer than |
> | & ∙ is greater than & ∙ is more than |
≤ | & ∙ is less than or equal to & ∙ is at most & ∙ is no more than |
≥ | & ∙ is greater than or equal to & ∙ is at least & ∙ is no less than |
With an inequality, it is possible to compare any combination of two numbers, variables, numeric expressions, or algebraic expressions.
Symbol | Example | Meaning |
---|---|---|
< | x<1 | The variable x is less than 1. |
≤ | x+1 ≤ -3 | The algebraic expression x+1 is less than or equal to - 3. |
> | 2x-5 > 5 | The expression 2x-5 is greater than 5. |
≥ | x ≥ 2x+1 | The variable x is greater than or equal to the expression 2x+1. |
This lesson will focus on inequalities of the following forms, where a is a number.
xa, x ≤ a, and x ≥ aAn inequality that compares two quantities that are strictly not equal is called a strict inequality. There are two types of strict inequalities. Less Than:&< Greater Than:&> The boundary values in strict inequalities are not included in the solution set. On the other hand, an inequality that compares two quantities that are not necessarily different is called a non-strict inequality. There are two types of non-strict inequalities. Less Than or Equal To:&≤ Greater Than or Equal To:&≥
The boundary values in non-strict inequalities are included in the solution set.Kevin and his father manage to find a boat so that the two of them can go fishing.
at least?
more than?
The number fish Kevin wants to catch is at least 7.
Let f be the number of fish Kevin wants to catch. The key phrase in the sentence is is at least.
This phrase represents the inequality symbol ≥. Then, the inequality can be written as follows.
The number fish Kevin wants to catch & is at least & 7. f & ≥ & 7
Therefore, the inequality is f ≥ 7.
The length of gray mullets must be longer than 11 inches.
Let g be the length of the gray mullet they are allowed to keep. The key phrase in this case is longer than.
This phrase can also be interpreted as more than.
It follows that the inequality symbol to use is >. Then, the inequality could be written as follows.
The length of gray mullets must be longer than 11 inches. ⇓ g > 11
The inequality is g > 11.
A solution of an inequality is any value of the variable that makes the inequality true. As an example, consider the following inequality. 2x-3< 5 Notice that if 0 is substituted for x in the inequality, the inequality holds true. Therefore, it can be said that 0 is a solution to the given inequality. 2( 0)-3 ? <5 ⇒ - 3 < 5 ✓
However, this is not the only value that makes the inequality true. There are other x-values like 1 and 2 that make it true. The set of all possible values that satisfy an inequality is the solution set of an inequality.The applet shows an inequality of the form xa, x ≤ a, or x≥ a. Determine if the given number is a solution to the inequality shown.
Inequalities can have an unlimited number of solutions — in other words, they might have infinitely many solutions. In such cases, number lines can be useful for showing all the values that make the inequality true. Consider graphing the solution set of the following inequality.
x ≥ - 6
The inequality is read as x is greater than or equal to - 6.
It is a non-strict inequality, so x=-6 is a solution. There are two possible cases when representing a number on a number line.
For the given inequality, a closed circle (∙) is placed at - 6 because it is a solution.
Every value of x greater than - 6 has to be included in the graph. Since greater numbers lie to the right on the number line, this is graphed as an arrow pointing to the right.
Kevin caught as many fish as he wanted in less than 5 hours.
is at least?
The amount of time spent fishing is less than5hours.
Let t be the amount of time that Kevin spent fishing. The key phrase in the sentence, is less than,
is represented by the symbol <. This means that the inequality can be written as follows.
The amount of time spent fishing & is less than & 5 hours. t & < & 5
The inequality t < 5 represents the situation.
t < 5
The inequality is read as t is less than 5.
This is a strict inequality, so x=5 is not a solution. Since 5 is not a solution, an open circle ∘ is used at that point.
Every value of t less than 5 has to be included in the graph. Since smaller numbers lie to the left on the number line, this is graphed as an arrow pointing to the left.
This is the graph of the inequality.
After sitting in the boat for so long, Kevin wants to go for a walk by the lake. He is curious about how far he and his father can throw stones.
Notice that there is a closed circle on the graph at 17. This means that k=17 is a solution of the inequality. This also means that the graph represents a non-strict inequality.
A closed circle (∙) is used. ⇓ Inequality symbol is either ≤ or ≥.
The arrow pointing toward the left indicates that all values less than 17 are also part of the solution set. Therefore, the inequality would be k is less than or equal to 17.
This can be expressed algebraically as follows.
kis less than or equal to17. ⇓ k ≤ 17
In the context of the question, this inequality means that Kevin can throw a stone at most 17 yards.
An open circle is placed at 35, so f=35 is not a solution of the inequality. This means that the graph represents a strict inequality.
An open circle (∘) is used. ⇓ Inequality symbol is either < or >.
The arrow pointing toward the left of the line indicates that all values less than 35 are part of the solution set. Therefore, the inequality would be f is less than 35.
This can be expressed algebraically as follows.
fis less than35. ⇓ f < 35
This inequality means that Kevin's father can throw a stone no farther than 35 yards.
Examine the given graph and determine its inequality.
Similar to equations, inequalities are mathematical expressions. Inequalities are useful for modeling a constraint or condition in a real-world problem. Consider the situation presented at the beginning of the lesson. Boats are rented to groups of tourists on the lake where Kevin and his father go fishing.
Two facts are known about the boats. Each boat can carry up to 600 pounds and hold up to five people.
up to.Is the given number a solution to the inequality?
The total weight of a group of people is at most 600 pounds. ⇓ w ≤ 600 The inequality w ≤ 600 represents the situation. It is a non-strict inequality, so x=600 is a solution. Since 600 is a solution, use a closed circle (∙) at thsi point on the number line.
Every value of w less than 600 has to be included in the solution set on the graph. Since smaller numbers lie to the left on the number line, this is graphed as an arrow pointing to the left.
This is the graph of the inequality.
The number of people is at most 5. ⇓ p ≤ 5 The inequality p ≤ 5 represents this situation. This is also non-strict inequality, so x=5 is a solution. Since 5 is a solution, a closed circle (∙) is used on the graph.
Every value of p less than 5 has to be included in the solution set. Since smaller numbers lie to the left on the number line, this is graphed as an arrow pointing to the left.
In the examples solved throughout this lesson, the variables are considered as real numbers and conditions other than those specified in the examples are ignored. For example, a negative number of people or any partial number of people would not make sense in Part B of this exercise. These constraints can be added to the solution set. p ≤ 5, wherep is a non-negative integer Now see what would happen to the graph if these additional constraints were added to the solution set.
Now go through the examples again and determine in which examples negative values are meaningless or only integers make sense for the solution sets.
Write the given sentence as an inequality.
Let's recall some key phrases that we can replace with inequality symbols.
Key Phrases | Symbol |
---|---|
& ∙ is less than & ∙ is fewer than | < |
& ∙ is greater than & ∙ is more than | > |
& ∙ is less than or equal to & ∙ is at most & ∙ is no more than | ≤ |
& ∙ is greater than or equal to & ∙ is at least & ∙ is no less than | ≥ |
The key phrase in the given sentence is is no less than.
We can replace this phrase with the inequality symbol ≥. Let's write the sentence as an inequality.
A numberq & is no less than & - 12.
q & ≥ & - 12
The inequality is q ≥ - 12.
Let's look for the key phrases and determine where we need to place the inequality symbol.
A numberz is less than 13.
We can see that the sentence contains the key phrase is less than.
We can use the inequality symbol < for ths phrase.
A numberz & is less than & 13.
z & < & 13
Use substitution to determine which value(s) from the given set makes the given inequality true. Select all that apply.
Let's start by reading the given inequality.
Inequality: t < 10
It is read as t is less than 10.
This means that all values of t less than 10 make the inequality true. When we look at the numbers in the given set, we can see that only 9.1 is less than 10. The other numbers are greater than 10.
rc
Inequality: & t < 10 [0.5em]
Set: & { 9.1,10.1,11 }
We can also use the substitution to determine the answer.
Value of t | t < 10 | Is the Inequality True? |
---|---|---|
9.1 | 9.1 < 10 | Yes |
10.1 | 10.1 ≮ 10 | No |
11 | 11 ≮ 10 | No |
From the given set, only 9.1 makes the inequality true.
Let's examine the inequality.
Inequality: y ≥ 5
It is read as y is greater than or equal to 5.
This means that all values of y greater than or equal to 5 make the inequality true. When we look at the numbers in the given set, we can see that 5 is equal to 5 and 10 is greater than 5.
rc
Inequality: & y ≥ 5 [0.5em]
Set: & {0, 5, 10 }
The answers are 5 and 10. Let's use substitution to check our answer.
Value of y | y ≥ 5 | Is the Inequality True? |
---|---|---|
0 | 0 ≱ 5 | No |
5 | 5 ≥ 5 | Yes |
10 | 10 ≥ 5 | Yes |
From the given set, 5 and 10 make the inequality true.
Identify the graph of the given inequality.
x ≤ 52
- 7 ≤ c
Let's graph the given inequality on a number line.
x ≤ 52
We can read the inequality as x is less than or equal to 52.
From this sentence, we can understand that 52 is a solution of the inequality. This means that we use a closed circle to represent the number on the number line.
The solution set of the inequality also includes the numbers less than 52. Since smaller numbers lie to the left on the number line, we can graph these solutions as an arrow pointing to the left.
This graph matches with the graph in option B.
We want to graph the inequality on a number line.
- 7 ≤ c
We read the inequality as - 7 is less than or equal to c.
We can conclude that - 7 is a solution to the inequality because the inequality is true when we substitute - 7 for c.
- 7 ≤ - 7 ✓
We use a closed circle to represent it on the number line.
The solution set of the inequality also includes the numbers greater than - 7. Since greater numbers lie to the right on the number line, we can graph these solutions as an arrow pointing to the right.
This graph matches with the graph in option A.
Write an inequality with the variable x that represents the graph.
We want to write an inequality for the given graph using the variable x.
From the graph, we can see that there is an open circle at - 1. Since an open circle is used to indicate a number that is not a solution to an inequality, the number - 1 is not a solution. This means that we need to write a strict inequality.
An open circle (∘) is used.
⇓
Inequality symbol is either < or > .
We also see that the arrow is pointing to the left. This indicates that all values less than - 1 form the solution set. We can express the inequality as x is less than - 1.
xis less than -1.
⇓
x < - 1
We will write an inequality that represents the following graph using the variable x.
We can see that there is an open circle at - 5. Since open circles are used for numbers that are not solutions of inequalities, the number - 5 is not a solution and our inequality is a strict inequality. An open circle (∘) is used. ⇓ Inequality symbol is either < or >. Since the arrow is pointing to the right, all values greater than - 5 form the solution set. As a result, the graph represents the values x is greater than - 5. xis greater than -5. ⇓ x > - 5