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Tuesday, March 26, 2013

Getting Back to the Basics

Order of Operations 

I have been working on order of operations with both the fifth and sixth graders at my school.  This is something I see students (AND ADULTS!!!) struggle with every year.  

Quick Quiz

1 + 1 + 1 + 1 + 1 + 1 x 0 + 1 = ???????

Was your answer 1?

Than you need to work on your order of operations!  
The answer you should have gotten was 6! 
Order of operations puts multiplication before addition. 

A lot of students/teachers use the acronym PEMDAS
P = parenthesis
E = exponents
M = multiplication
D = division
A = addition
S = subtraction 

PEMDAS can cause its own problems
Here is another one that gets people

Quick Quiz 2

48 / 6 x 8 = ?????

Did you get 1?

You made a very common mistake for those who love PEMDAS.  The problem with PEMDAS is that it makes it seem like multiplication comes before division because it comes first in the acronym.  But REALLY with order of operations, multiplication and division are on the same level.  They should be done simultaneously from left to right.  So on Quick Quiz 2 you should have done 48 / 6 = 8 and then done 8 x 8 = 64.  Much different answer!

Try one more.  I am sure I won't be able to get you again!

Quick Quiz 3

25 - 5 + 80 =

If you got - 60, you fell for the PEMDAS trick again.  Addition and subtraction are on the same level for order of operations just like multiplication and division.  You need to do them simultaneously from left to right.  So 25-5 = 20 and then you add 80.  If you got 100, good for you!

How do you help students with order of operations??? 


  1. You're right, this is tough for kids AND adults!! It is especially difficult for them to remember that +/- and x/div. should be done from left to right. Never liked the PEMDAS acronym......great little lesson!

    I got them all correct, btw! ;)

    Tales of Frogs and Cupcakes

    1. Good for you! I did this at a staff meeting last year and was amazed by how many folks got them wrong (especially those PEMDAS people!)