The order of operations - two video lessons for pre-algebra
In the first video (below) I start out with a mini-review of exponents and then we study the order of operations (PEMDAS rule), followed by a few solved examples.
The lesson explains how to solve these problems using the correct order of operations:
- 102 − 82
- (10 − 8)2; notice this is very similar to the expression above but the parenthesis makes a big difference.
- 24 − 23 / 4
The acronym PEMDAS (or Please Excuse My Dear Ant Sally) comes from:
Parentheses
Exponents & roots
Multiplication & Division
Addition & Subtraction
In the second part we will solve more challenging examples that have more operations than the ones in part 1. The expressions include exponents plus other operations. In these examples, divisions are written with a fraction line, which means that the division is done last. It is as if there were parentheses around the numerator and the denominator.
I also explain why we can do multiplications and divisions in any order IF the expression only contains multiplications & divisions, and no other operations. This boils down to the fact that each division can be written as a multiplication by the reciprocal of the divisor.
In my last example, we touch on decimal operations (decimal multiplication & division).
See also
Math Mammoth Grade 7 curriculum (pre-algebra)