2. Numerical Expressions
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Chapter 4
2.
Numerical Expressions
This lesson provides a thorough understanding of numerical expressions, emphasizing the importance of the order of operations and the PEMDAS rule. It explains how these principles are crucial for solving mathematical problems accurately. For example, the order of operations ensures that calculations are performed in a specific sequence to avoid errors. The acronym PEMDAS, which stands for Parentheses, Exponents, Multiplication, Division, Addition, and Subtraction, serves as a helpful mnemonic for remembering this sequence. These concepts are not just theoretical; they have practical applications in various fields such as engineering, finance, and data analysis. Overall, the material is a valuable lesson for anyone interested in mastering the intricacies of numerical expressions and their real-world applications.
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Lesson Settings & Tools
| | 10 Theory slides |
| | 10 Exercises - Grade E - A |
| | Each lesson is meant to take 1-2 classroom sessions |
Numerical Expressions
Slide of 10
The basic mathematical operations make up most of the mathematical ideas applied to the real world. Generally, these operations are combined in different ways to express different things. The goal of this lesson is to show how to evaluate a set of mathematical operations.
Catch-Up and Review
Here are a few recommended readings before getting started with this lesson.
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Challenge
Which Result is Correct?
If a mathematical operation is done correctly, there is always a single correct result. When adding two numbers, there is only one correct value for the sum. 3 + 2 = 7 * 3 + 2 = 5 ✓ The same happens when two numbers are multiplied. If the multiplication is done correctly, the result is correct. 2* 5 = 13 * 2* 5 = 10 ✓ But what happens if multiple operations are combined? Izabella and Kriz are discussing how to solve an expression that includes both addition and multiplication. 3 + 2 * 5 Izabella says that the operations should be done left to right. Here is how she evaluated the operations.
But Kriz thinks that the multiplication should be done first. This is how Kriz evaluated the operations.
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Discussion
Numerical Expressions
A numeric expression, or numerical expression, is a sequence of mathematical operations that only involves numbers. Consider the following examples.
| Example | Is It a Numeric Expression? |
|---|---|
| 5+3-2*8 | ✓ |
| (9+12)^3 -4* 7 | ✓ |
| 3/7 + [(5-1)* (7+ 4)]^5 - 1/7 | ✓ |
| 9w^2+4s+7 | * |
| 1125 | * |
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Pop Quiz
Identifying Numerical Expressions
Select whether each given expression is a numerical expression or not.
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Discussion
Order of Operations
The order of operations is the order to follow when evaluating an expression that has more than one operation. The order of operations can be described as a series of steps.
Consider this expression to see the steps in action.
(1+2)* 3^2-5+5/2 = ?
The example expression contains a set of parentheses, an exponent, multiplication, division, addition, and subtraction. The expression is evaluated following the order of operations.
| Expression | Simplified | Operation |
|---|---|---|
| (1+2)* 3^2-5+5/2 | 3* 3^2-10/2 | Evaluating Parentheses and Grouping Symbols |
| 3* 3^2-10/2 | 3* 9-10/2 | Exponents |
| 3* 9-10/2 | 27-5 | Multiplication and Division |
| 27-5 | 22 | Subtraction |
There are a few things to note about this evaluation.
- The addition in the numerator of 5+52 was evaluated at the same time as the expression between parentheses (1+2). This is because fraction bars are grouping symbols like parentheses.
- The order of operations must be followed when evaluating expressions in grouping symbols.
- Operations that are inverse and at the same level must be evaluated from left to right. This rule applies for multiplication and division and for addition and subtraction.
To remember the order of operations, it is useful to memorize the acronym PEMDAS. Each letter of PEMDAS indicates a set of operations. A fun sentence to remember this acronym is Please Excuse My Dear Aunt Sally.
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Example
Baseball Practice
While waiting for baseball practice to start, Zain passed the time by counting how many people arrived to the field to practice and how many people left the field.
When Zain arrived and started counting, there were 9 people on the field practicing. Before Zain's practice started, two groups of three people left and four groups of six people arrived to the field. Then Zain's practice started.
a Write a numerical expression of the number of people in the field.
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b How many people were at Zain's practice that day?
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Hint
a Consider the given information carefully. What is the first number of people in the field?
b Follow the order of operations.
Solution
a To write the numerical expression, it is important to consider the given information carefully. First, it is given that there were 9 people on the field when Zain started counting. Write this number as the first part of the numerical expression.
9 Then, 2 groups of 3 people left. The 2 groups of 3 people can be written as the product of 2 times 3. Since these people are leaving, the product is subtracted from 9. 9 - 2* 3 Finally, 4 groups of 6 people arrived to the field. This number of people can be written as the multiplication of 4 times 6. This time the product is added because the people are arriving. 9 - 2* 3 + 4* 6 This is a complete numerical expression to find the number of people at the field when Zain's practice started.
b The order of operations must be followed to evaluate the numerical expression found in Part A. The acronym PEMDAS is useful to recall the order of operations.
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Example
Baseball Equipment
Zain's baseball team needs new equipment before the season starts. Since Zain lives close to a good baseball equipment store, they were in charge of checking the prices. They noted these prices in a table.
| Item | Price |
|---|---|
| Bat | $200 |
| Glove | $95 |
| Uniform | $130 |
Zain's team need 2 new bats, 8 new gloves, and 4 new uniforms. Luckily, there is a sale going on where bats and gloves are half their regular prices. Zain also has a $100 discount coupon that they will give the coach for equipment.
a Write a numerical expression for the total cost of the equipment that Zain's team needs.
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b Evaluate the expression to find how much money Zain's team needs to buy the equipment.
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Hint
a Consider the given information carefully. The total cost per group of items can be written as a product.
b Remember the order of operations.
Solution
a Start by carefully considering the given information. It is given that Zain's team needs 2 new bats. Since each bat costs $ 200, the total cost of the bats is the multiplication of 2 and 200.
2* 200 Next consider the cost of the gloves. Each glove has a price of $ 95. Since Zain's team needs 8 new gloves, the gloves have a cost the product of 95 and 8. Add this product to the cost of the bats. 2*200 + 95* 8 Before adding the cost of the uniforms, it is important to remember that there is a sale going on that affects the cost of the bats and the gloves. To group this total, we can add parentheses to the addition. (2*200 + 95* 8) The sale reduces this total by half, which can be written as multiplying the total by 12. 1/2*(2*200 + 95* 8) The total cost of the uniforms is the product of the number of uniforms and the price per uniform. The team needs 4 uniforms and the price of each uniform is $ 130. This product must be added to the expression above. 1/2*(2*200 + 95* 8) + 4* 130 Lastly, the discount from Zain's coupon reduces the cost by $100. This is written as a subtraction of 100. 1/2*(2*200 + 95* 8) + 4* 130-100
b The order of operations must be followed to evaluate the numerical expression from Part A. The steps of the order of operations can be remembered considering the acronym PEMDAS.
Extra
Using the Distributive PropertyThe Distributive Property was discussed in previews lessons. The expression can be solved differently by using this property.
The Distributive Property allows to remove the parentheses before simplifying the expression inside. The rest of the expression can be simplified regularly.
The result is the same as the previous one following the order of operations. But remember that the property only holds true when a number is multiplying the result of an addition. It is not always possible to use the Distributive Property, but it can be useful in some cases.
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Example
Zain at the Bat
Zain is having a great time at bat in today's baseball game. He is hitting every single ball!
a The height of the ball 2.75 seconds after Zain hit it is given by a numerical expression.
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b The distance that the ball traveled after the same 2.75 seconds can be found by using another numerical expression.
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Hint
a Follow the order of operations.
b Note that the only operation in the numerical expression is multiplication.
Solution
a To evaluate the expression, every operation must be done following the order of operations. The acronym PEMDAS is useful to remember each step.
b Looking at the given numerical expression, it can be noted the only operation present is multiplication.
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Pop Quiz
Evaluating Numerical Expressions
Write the value of each given numerical expression. Remember the order of operations!
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Closure
Finding the Correct Result
Two different numerical expressions were presented at the beginning of this lesson. The second expression has more operations than the first one. The good thing is that any numerical expression can be solved following the order of operations. The acronym PEMDAS is helpful for remembering the order!
The first numerical expression has both addition and multiplication.
3+2* 5
When evaluating this expression, Izabella and Kriz found different results.
rc
Izabella: & 25 Kriz: & 13
But the correct result is the one obtained following the order of operations. This means that the multiplication needs to be done first, then the addition.
The answer is 13. This means that Kriz was correct. The second numerical expression is more complex, but the procedure to evaluate it is the same. The first step is always to determine which operations are in the expression.
48 ÷ 8 +18/4^2 - 4
A fraction line works as a grouping symbol, like a set of parentheses. This means that the expressions of the denominator and the numerator have to be evaluated before dividing. Note that the denominator has an exponent, so this is the first operation to be performed.
48 ÷ 8 +18/4^2 - 4 ⇓ 48 ÷ 8 +18/16 - 4
Next, evaluate the division in the numerator.
48 ÷ 8 +18/16 - 4 ⇓ 6 +18/16 - 4
Next, calculate the addition and the subtraction, then divide the obtained values.
The value of the numeric expression is 2. Remember that it does not matter how simple or complex a numerical expression is — any numerical expression can be solved following the order of operations. That is the beauty of it!
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Numerical Expressions
Exercise 2.1
Tadeo solved the following numerical expression.
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We want to determine whether the answer that Tadeo ended up with is correct.
We can do this by solving the numerical expression ourselves by using the order of operations.
Remember that the symbols * and * are used to indicate multiplication. We will start by evaluating the number with the exponent, according to the order of operations.
The next step is to multiply 2 by 25. If we look at Tadeo's procedure, we can see that he added 11 and 2 before multiplying. This mistake is described in option A.
We can find the correct value by evaluating the expression by following the order of operations. Let's finish what we started in Part A by multiplying and then adding the remaining numbers.
The correct value is 61.
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Solution
Tearrik sells packs of cookies in two different sizes. The table shows the number of cookies in each pack.
| Bag | Number of Cookies |
|---|---|
| Large | 20 |
| Small | 6 |
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We are asked to write a numerical expression for the total number of cookies. Let's consider the given information. Let's start by making a table to visualize how many cookies there are in each size of packs.
| Bag | Number of Cookies |
|---|---|
| Large | 20 |
| Small | 6 |
We are told that there are 8 large packs and 13 small packs of cookies. To find the total number of cookies in the large packs, we need to multiply the number of large packs by the number of cookies in each large pack. Cookies in Large Packs: 8*20 We can find the number of cookies in the small packs in a similar fashion. This time we multiply the number of small packs by the number of cookies in each small pack. Cookies in Small Packs: 13* 6 Now we have expressions for the total number of cookies in both the large and small packs. Things are going great. Now we add the expressions for the number of cookies in each pack size so we can find the numerical expression to find the total number of cookies. 8*20 + 13* 6 Good job!
Now we want to find the total number of cookies in the packs. We can evaluate the expression from Part A to do this. In order to evaluate the expression correctly, we need to follow the steps of the order of operations.
Now let's carefully consider the numerical expression that we wrote in Part A.
8*20 + 13* 6
We can see that the expression does not have any parentheses or exponents, but there are two multiplications and an addition. Following the order of operations, we should do the multiplications from left to right and then we add the resulting numbers. Let's do it!
The value of the expression is 238, which means that there are 238 cookies in the packs. We did it!
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Solution
Vincenzo bought some strawberries for an event. He bought 3 and 12 bags of strawberries.
Each bag of strawberries has a weight of 456 grams and each strawberry has a weight of 12 grams.
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We want to write an expression for the total number of strawberries that Vincenzo bought. We know that he bought 3 and 12 bags of strawberries. Let's write this as an expression. Number of Bags:( 3 + 1/2) The total number of strawberries purchased is the product of the number of bags by the number of strawberries per bag. ( 3 + 1/2)* Strawberries per Bag Now we need to find the number of strawberries per bag. Each bag weighs 456 grams and each strawberry weighs 12 grams. The number of strawberries per bag can be found by dividing 456 by 12. Strawberries per Bag:456/12 We now have an expression for the number of strawberries per bag. Things are going great! To finish writing the expression total expression for how many strawberries Vincenzo bought, we will multiply the number of bags by the number of strawberries per bag. ( 3 + 1/2)*456/12 We did it!
Consider the numerical expression we wrote in Part A.
( 3 + 1/2)*456/12
Before we solve it, let's review the order of operations to be sure we solve it correctly.
Our expression has a set of parentheses, so we will start by solving the addition between them. Remember that any integer can be rewritten as a fraction with a denominator of one.
This fraction can be substituted for the expression between parentheses. 7/2*456/12 The result is the multiplication of two fractions. To multiply two fractions, we multiply their respective numerators and denominators. Let's do it!
We found that Vincenzo bought 133 strawberries.
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Numerical Expressions
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