PEMDAS or in my case PPPPPPPPEMDAS

I do a lot of excel math at work and I definitely over parenthesis!  I put parenthesis around everything I know should be together...because I am not sure how excel will calc things...because I am definitely not super strong with the order of operations!


Order of operation starts in the 5th grade in common core:

Write and interpret numerical expressions.

CCSS.MATH.CONTENT.5.OA.A.1
Use parentheses, brackets, or braces in numerical expressions, and evaluate expressions with these symbols.

Many people will use the tool PEMDAS for order of operations:

PEMDAS

Parenthesis

Exponents

Multiplication

Division

Addition

Subtraction

Seems easy?  Not so much!

Multiplication and division are basically the same thing (multiplying by a fraction is division, adding negative numbers is subtraction) so it doesn't really work to always do M before D or A before S.

The correct way is to do PE then M/S right to left and then A/S right to left.  It is not as easy as just PEMDAS.

One way to think about this is to think about what is the most powerful operation and go from powerful to weak.  Giving a number an exponent is POWERFUL

3³ is 27 - POWERFUL! 

3x3 is 9 less powerful or 3/3 =1

3+3 is 6 least powerful/weak or 3-3 =0

When these rules are followed you otherwise just go right to left.

Some examples:

4 ÷ 2 · 5 

Following the order of operations, because these are just multiplication and division and we know they are just the inverse of each other, we work right to left:

4 ÷ 2=2· 5=10

However, consider this problem:

3+4x2 we have to use our PEM/DA/S

Multiplication is more powerful than addition so I want to do that first, 4x2=8 and then i do the addition, 3+8 = 11

Once you get the hang of it and understand powerful to weak it becomes more clear, but practice will help get this point across