How to write "this per that" in mathematical terms? What is the mathematical equivalent of saying, for example, meters per second? If we want to say that something moves with the rate of 50 meters per 30 seconds--do we write this as a fraction or as an equation, or we can write as both? I mean what is the difference between saying "50 m/30 sec" and "50 m = 30 sec"? I'm confused.