Math
posted by Marcus on .
How would proportions be used to "scale up" or "scale down" something?
(Not really sure if I even understand what this means. I even read my text and I can't figure this out.)

Let's say that you have a concentrated disinfectant that says that you should mix one cup of disinfectant to one quart of water  but you need one gallon (sixteen cups) of water plus the added disinfectant to make enough of the mixture. Your proportion would be 1 cup of disinfectant to 4 cups of water, since a quart is four cups. Using this ratio, or proportion, you can scale the amount up to what you need: 1/4 = x/16, where x is the amount of disinfectant (which would be 4 cups).
If you need to use less water than the quart, you can use the same ratio to scale down your amount. Let's say that, instead of a quart, you want to use only two cups of water. You would now need: 1/4 = x/2, where x is again the amount of disinfectant (which would now be only 1/2 of a cup). This is how proportions can be used to scale something up or down.