When you start studying algebra, you will also study how two (or more) variables can relate to each other specifically. The cases you’ll study are:
Direct Variation , where both variables either increase or decrease together
Inverse or Indirect Variation, where when one of the variables increases, the other one decreases
Joint Variation , where more than two variables are related directly
Combined Variation, which involves a combination of direct or joint variation, and indirect variation
These sound like a lot of fancy math words, but it’s really not too bad. Here are some examples of direct and inverse variation:
Direct : The number of dollars I make varies directly (or you can say varies proportionally) with how much I work.
Direct : The length of the side a square varies directly with the perimeter of the square.
Inverse : The number of people I invite to my bowling party varies inversely with the number of games they might get to play (or you can say is proportional to the inverse of ).
Inverse : The temperature in my house varies indirectly (same as inversely) with the amount of time the air conditioning is running.
Inverse : My GPA may vary directly inversely with the number of hours I watch TV.
P.S You got the drill? This is not to expressly treat variation but to introduce it to you.