 ## Lesson Tutor : Algebra Lesson Grade 9 Order of Operations

/  Lesson Tutor : Algebra Lesson Grade 9 Order of Operations

Basic Algebra – Lesson 4
by Elaine Ernst Schneider

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:

Outline:

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.

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