Oh... but you could take “12% * 20”, or “12/100 * 20”. I think it's important to teach understanding that “percent” means “per hundred” or “division by hundred” instead of just teaching to rewrite. Rewriting can be useful, but it isn't necessary.
It's also useful to know that you can shorten “/100” to “%” in any longer equations.
I agree with blackcat; you can't multiply "12% * 20" directly because the two terms have different units. The % sign indicates that the 12 is on a scale that the 20 isn't on.
You need to include a conversion factor first, which you're doing with the fraction, but maybe not realizing that this is what you're doing. (?) The conversion to 12/100 puts the percent on the same scale as the 20.
This is a concept that a learner needs to understand completely in order to internalize these ideas. A teacher needs to be able to explain what's going on and how things work; you're not (but blackcat has been saying this consistently).
I taught this stuff to my DD about a year ago. We went one skill at a time, and she was able to to perform each operation easily. The problems started when a bit of time passed and she was confronted with a variety of problems. Some were straightforward operations, and some were word problems. She had trouble seeing the forest for the trees. I taught her some second-level ideas (e.g. conversion factor) that helped her see how everything related to each other.
The same thing happened a month ago with mixture problems. After she struggled through some of them, she had a vague idea of what was going on. I then showed her that they're all based on C1V1 = C2V2 and that if you add something to the first side, you have to add it to the second one. This ties nicely with that basic stuff she learned when she was learning to solve equations: if you add something to one side, add it to the other.
