Hi There!
PEMDAS is a term in math in order of operations.
Here is what this means
Paranthesis
exponents
multiplication/division (left to right)
addition/subtraction (left to right)
In order of operations, you use pemdas in order so the P, would come first, E second, and so on.
Example 1: (10+9)-1, in this example, since parenthesis is first you would solve 10+9=19 and then you would subtract that by one 19-1=18
In conclusion this is the rule of pemdas.
Hope this helps :)