Ahh, that's a really good point! I forget about the "X% of Y = Y% of X"
Honestly, I normally just use a calculator quick (move the decimal twice, multiply and all that jazz) for weird percentages or I want a precise answer.
But I like knowing different ways of thinking about it because it can become easier than using a calculator (with practice). And it's fun, cause I'm a bit of a math nerd