This actually depends in different problem but the way I think your talking about is the easiest way.
Problem: 80% of 385
Step 1 You will be Multiplying
Step 2. Move the decimal to the left by 2 places.
Example: 385
x .80
----------
Step 3 do the problem
example: 385
x.80
-----------
308.0% is the percentage
make sure to drop the decimal but if there there nothing after it don't leave it in your final answers ( some teachers mark it wrong when it really it's not wrong just improper format)
The reason for this answer is algebra. Since you give a full explanantion on it I'm not sure if I answered it correctly. But here is what I think from what you gave of the question.
