Another way you can do unit conversions is to use ratios.
Here’s how it works. The relationship "16 cups is equivalent to 1 gallon" can be written as the ratio 16 cups : 1 gallon. And since the quantities are equal, you can write the ratio either way—cups to gallons, or gallons to cups, as shown below.
Now, if you want to convert 320 cups to gallons, then you write the ratio as a fraction. Write the number of gallons on top (the numerator) and cups on the bottom (the denominator). You will see why in a moment! Then multiply:
You can cross out the "cups" measurement because it appears in the numerator and denominator. Notice that once you do that, you are left with gallons—the unit you were looking for!
Remember that 320 gallons/16 is the same as 320 gallons ÷ 16, or 20 gallons. You end up dividing, just as Noreen did in the video.