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Order of Operations

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Abigail buys 2 shirts at $12 apiece. She also buys a pair of jeans that were orginally$50 but are discounted by 15%. If her total purchase is over $60, she will get an additional$10 off. How much was her bill?

Guidance

The properties of algebra enable us to solve mathematical equations. Notice that these properties hold for addition and multiplication.

Property Example
Commutative $a+b=b+a,ab=ba$
Associative $a+(b+c)=(a+b)+c,a(bc)=(ab)c$
Identity $a+0=a,a \cdot 1=a$
Inverse $a+(-a)=0,a \cdot \frac{1}{a}=1$
Distributive $a(b+c)=ab+ac$

From the Identity Property, we can say that 0 is the additive identity and 1 is the multiplicative identity. Similarly, from the Inverse Property, $-a$ is the additive inverse of $a$ and $\frac{1}{a}$ is the multiplicative inverse of $a$ because they both equal the identity.

Example A

Identify the property used in the equations below.

a) $2(4x-3)=8x-6$

b) $5 \cdot \frac{1}{5}=1$

c) $6 \cdot (7 \cdot 8)=(6 \cdot 7) \cdot 8$

Solution:

a) is an example of the Distributive Property,

b) is an example of the Inverse Property, and

c) is an example of the Associative Property.

More Guidance

Going along with the properties of algebra, are the Order of Operations. The Order of Operations is a set of guidelines that allow mathematicians to perform problems in the exact same way. The order is as follows:

Parenthesis Do anything in parenthesis first.

Exponents Next, all powers (exponents) need to be evaluated.

Multiplication/Division Multiplication and division must be done at the same time, from left to right, because they are inverses of each other.

Addition/Subtraction Addition and subtraction are also done together, from left to right.

Example B

Simplify $2^2+6 \cdot 3-(5-1)$ .

Solution:

Parenthesis $\rightarrow 2^2+6 \cdot 3-4$

Exponents $\rightarrow 4+6 \cdot 3-4$

Multiplication $\rightarrow 4+18-4$

Add/Subtract $\rightarrow 18$

Example C

Simplify $\frac{9-4 \div 2+13}{2^2 \cdot 3-7}$ .

Solution: Think of everything in the numerator in its own set of parenthesis as well as everything in the denominator. The problem can be rewritten as $(9-4 \div 2 +13) \div (2^2 \cdot 3-7)$ . When there are multiple operations in a set of parenthesis, use the Order of Operations within each set.

$&(9-4 \div 2 +13) \div (2^2 \cdot 3-7)\\&(9-2+13) \div (4 \cdot 3-7)\\&(7+13) \div (12-7)\\& 20 \div 5\\&4$

Parenthesis can also be written within another set of parenthesis. This is called embedding parenthesis. When embedded parenthesis are in a problem, you may see brackets, [ ], in addition to parenthesis.

Intro Problem Revisit If we don't have the Order of Operations, Abigail could get very confused and not have the right amount of money to pay for her items. So, the two shirts are $24 $(2 \cdot 12)$ and only the jeans are discounted. They are $50-0.15\cdot 50 = 42.50$ . Adding these two items together, we get that her total bill is$24 + $42.50 =$66.50. So, because her purchase is over $60, she gets an additional$10 off, making her final bill \$56.50.

Guided Practice

What property is being used?

1. $5(c - 9) = 5c - 45$

2. $6 \cdot 7=7 \cdot 6$

3. Use the Order of Operations to simplify $8+[4^2-6 \div (5+1)]$ .

1. 5 is being distributed to each term inside the parenthesis, therefore the Distributive Property is being used.

2. Here, order does not matter when multiplying 6 and 7. This is an example of the Commutative Property.

3. This is an example of embedded parenthesis, as discussed above. Start by simplifying the parenthesis that are inside the brackets. Then, simplify what is inside the brackets according to the Order of Operations.

$&8+[4^2-6 \div (5+1)]\\&8+[4^2-6 \div 6]\\&8+[16-6\div 6]\\&8+[16-1]\\&8+15\\&23$

Vocabulary

A number that is the opposite sign of a given number, such that, when added, their sum is zero.
Multiplicative Inverse
A number that is the reciprocal (and same sign) of a given number, such that, when multiplied, their product is 1.
Multiplicative Identity
The multiplicative identity is 1.
The Order of Operations
A set of guidelines used to simplify mathematical expressions. When simplifying an expression, the order is perform all operations inside any parenthesis first, followed by evaluating all exponents. Third, do all multiplication and division at the same time, from left to right. Lastly, do all addition and subtraction at the same time, from left to right.
Evaluate
Solve.
Simplify
To combine like terms within an expression to make it as “simple” as possible.

Practice

Determine which algebraic property is being used below.

1. $8 + 5 = 5 + 8$
2. $7(x - 2) = 7x - 14$
3. $\frac{2}{3} \cdot \frac{3}{2}=1$
4. $4 \cdot (5 \cdot 2)=(4 \cdot 5) \cdot 2$
5. $-\frac{1}{4}+0=-\frac{1}{4}$
6. $-6+6=0$
7. What is the additive inverse of 1?
8. What is the multiplicative inverse of $-\frac{1}{5}$ ?
9. Simplify $6(4-9+5)$ using:
1. the Distributive Property
2. the Order of Operations
3. Do you get the same answer? Why do you think that is?

Simplify the following expressions using the Order of Operations.

1. $12 \div 4+3^3 \cdot 2-10$
2. $8 \div 4+(15 \div 3-2^2) \cdot 6$
3. $\frac{10-4 \div 2}{7 \cdot 2+2}$
4. $\frac{1+20-16 \div 4^2}{(5-3)^2+12\div 2}$
5. $[3+(4+7 \cdot 3)\div 5]^2-47$
6. $\frac{7 \cdot 4-4}{\frac{6}{2}+5} \cdot 4^2-18$
7. $6^2-[9+(7-5)^3]+49 \div 7$
8. $\frac{27 \div 3^2+(6-2^2)}{(32 \div 8+1) \cdot 3}$
9. $6+5 \cdot 2-9 \div 3+4$
10. Using #18 above, insert parenthesis to make the expression equal 1. You may need to use more than one set of parenthesis.
11. Using #18 above, insert parenthesis to make the expression equal 23. You may need to use more than one set of parenthesis.