Cool Mathematical Trick

x% of y = y% of x

An easy example: Let x=10, y=60.
Then x% of y -- 10% of 60 -- is 6.
But y% of x -- 60% of 10 -- is also 6.

Those calculations are rapidly performed in your head. But what if the calculation is just a little more difficult: What is 4% of 75?

You can divide 75 by 100 to get .75, and multiply by 4: .75x4=3

Or you can flip the equation; instead of doing 4% of 75, do 75% of 4.