Definition: PEMDAS is a memory aid for the order of operations: Parentheses, Exponents, Multiplication and Division, then Addition and Subtraction.
What does PEMDAS stand for?
Each letter is a step: Parentheses, Exponents, Multiplication, Division, Addition, Subtraction. Students often remember it with the sentence Please Excuse My Dear Aunt Sally.
What does it hide?
The letters suggest six steps, but there are four levels. Multiplication and division share a level, and so do addition and subtraction. Within a level, work from left to right.
How do you use it?
Simplify 7 + 2 x (9 – 5)2 – 10.
- Parentheses: 9 – 5 = 4.
- Exponent: 42 = 16.
- Multiplication: 2 x 16 = 32.
- Left to right: 7 + 32 = 39, then 39 – 10 = 29.
Which mistake does PEMDAS cause?
Reading it as strictly M before D. In 36 / 9 x 2, division comes first because it appears first, so the answer is 4 x 2 = 8. Doing the multiplication first would give 36 / 18 = 2, which is wrong.
Example: 20 – 3 x 4 + 23 = 20 – 12 + 8 = 16.