What is PEMDAS? – Definition, Rule & Examples

What Does PEMDAS Mean?

PEMDAS is an acronym for the words parenthesis, exponents, multiplication, division, addition, subtraction. Given two or more operations in a single expression, the order of the letters in PEMDAS tells you what to calculate first, second, third and so on, until the calculation is complete. If there are grouping symbols in the expression, PEMDAS tells you to calculate within the grouping symbols first.

The letters PEMDAS and the words parenthesis, exponents, multiplication, division, addition, subtraction may not be very meaningful for someone trying to remember this order, so a phrase has also been attached with the letters in PEMDAS: Please Excuse My Dear Aunt Sally. If you can remember this phrase, then it may be easier to remember the order of operations given in PEMDAS.

Why Is PEMDAS Important?

Without PEMDAS, there are no guidelines to obtain only one correct answer. As a very simple example, to calculate 2 * 4 + 7, I could multiply first, and then add to get 15. I also have the option to add first, then multiply and get 22. Which answer is correct? Using PEMDAS, the only correct answer is 15, because the order of the letters in PEMDAS tell me that multiplication, M, should be performed before addition, A.

Here’s an explanation of the rules given in PEMDAS:

1. P as the first letter means you complete any calculations in grouping symbols first.
2. Next, look for exponents, E. Ignore any other operation, and take any numbers with exponents to their respective powers.
3. Even though M for multiplication in PEMDAS comes before D for division, these two operations actually have the same priority. Complete only those two operations in the order they occur from left to right.
4. Even though A for addition is in PEMDAS before S for subtraction, these two operations also have the same priority. You look for these last two operations from left to right and complete them in that order.

Using PEMDAS in a Mathematical Expression

Example One:

If you are told to calculate or simplify the expression 24 + 6 / 3 * 5 * 2^3 – 9, how does PEMDAS work? First, I look for any grouping symbols (P). There are none, so I then look for any exponents (E). Since I see 2^3, I will do that calculation first, without performing any other calculation.

• 24 + 6 / 3 * 5 * 8 – 9

Now, I look for multiplication (M) and division (D) from left to right, ignoring any addition or subtraction. My next series of calculations will produce the following:

• 24 + 6 / 3 * 5 * 8 – 9
  • 24 + 2 * 5 * 8 – 9
    • 24 + 10 * 8 – 9
      • 24 + 80 – 9

Lastly, I complete addition (A) and subtraction (S) from left to right.

• 24 + 80 – 9 = 95

Example Two:

Calculate 36 – 2(20 + 12 / 4 * 3 – 2^2) + 10. Since there is a grouping symbol, I must perform all calculations in the parenthesis first, using PEMDAS for any operations in that expression.

• 36 – 2(20 + 12 / 4 * 3 – 2^2) + 10
  • 36 – 2(20 + 12 / 4 * 3 – 4) + 10
    • 36 – 2(20 + 3 * 3 – 4) + 10
      • 36 – 2(20 + 9 – 4) + 10
        • 36 – 2(25) + 10

Ignoring the addition and subtraction, I complete the one multiplication operation next.

• 36 – 2(25) + 10
  • 36 – 50 + 10

Last, I add and subtract from left to right.

• 36 – 50 + 10 = – 4

If you encounter a calculation with one expression grouped inside another grouping, start with the innermost grouped expression and work your outward, using PEMDAS.