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You are HERE >> Mathematics > Algebra > Grade 9

Basic Algebra - Lesson 4
by Elaine Ernst Schneider

Practical Algebra: A Self-Teaching Guide, 2nd Edition by Peter H. Selby, Steve Slavin, Steven Slavin
Algebra to Go : A Mathematics Handbook



Objective(s): By the end of this lesson the student will be able to: 
apply the order of operations to solve math equations.

Pre Class Assignment:  Completion of Algebra Lesson 3
Resources/Equipment/Time Required: 

In the first lesson, you learned that numbers and variables form sentences, or algebraic "expressions." When you take information from a sentence and turn it into a mathematical expression, it is called "translating." In another lesson, you learned that when you write algebraic expressions, use +, -, and = signs; and for division, use / , the same way you know that when you see a fraction, it means to divide the top number by the bottom number. Then, for multiplication, we learned to write the expression with no symbol or sign between them (such as 3a), with an X , or using parentheses. The parenthesis is especially useful in longer problems such as (3y)(4-2x). 

But what if there are no parentheses or brackets? How do you know which to do first? Add, divide, multiply?  Which one?

When there are no other indications as to which computation to do first, mathematicians follow The Order of Operations rule. Multiply, Divide, Add, Subtract. 

A good way to remember the Order of Operations is to think about My Dear Aunt Sally. The M is for multiply, the D in Dear is for Divide, the A is for Add, and the S in Sally is for subtract.

    HINT: If the problem has only multiplication and division, then work from left to right.

    HINT: If the problem has only subtraction and addition, then work from left to right.

    Let's Get Started:

             13 - 2 X 5

If I just do the math from left to right, I would say 13 - 2 = 11. Then 11 times 5 = 55.

But the Order of Operations tells me to multiply first! So, 2 X 5 = 10. Then, I subtract 10 from 13 and get 3. 

You can see that which order you choose makes a BIG difference in the answer! That's why it's important to follow the Order of Operations.

Now it's time for you to try a few. 

Assignment(s) including Answer key: 

               1.  10 - 4 + 3 
               2.  10 + 4 X 2 
               3.  (5 X 4) -15 + 2 
               4.  12 - 2(3 + 1) 
               5.  18 + 2(3) 
               6.  (12 - 2)(3 + 4) 
               7.  4 X 3 + 5 
               8.  24 - 6 +2 
               9.  24 - 6 X 2 
              10. 36/9 - 2

For Answer Key, Click Here

Pre-Requisite To:   Basic Algebra - Lesson 5 

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  • Submitted by:  © Elaine Ernst Schneider  is a freelance writer and a teacher. She has been writing since high school and has published articles, songs, and children's work. Presently, Elaine is a curriculum author for Group Publishing and also writes the City Songs column for ezine. 
    Send a note to Elaine.
    Please revise your: "My Dear Aunt Sally" to "Please Excuse My Dear Aunt Sally" from this link That way it includes parentheses and exponents.

    Just a suggestion but a good one I feel.

    Thanks, Dave (August, 2003)
    Send us your comments

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