1. Identify the variation as direct, inverse, joint or combined. s/t = c

directinversejoint combined

2. r=cs/t

3. I=MCN

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. Direct or Proportional Variation

When two variables are related directly, the ratio of their values is always the same. So as one goes up, so does the other, and if one goes down, so does the other. Think of linear direct variation as a "y = mx" line, where the ratio of y to x is the slope (m). With direct variation, the y-intercept is always 0 (zero); this is how it’s defined.

(Note that Part Variation, or "varies partly", means that there is an extra fixed constant, so we’ll have an equation like y=mx+b, which is our typical linear equation.)

Direct variation problems are typically written:

→ y = kx where k is the ratio of y to x (which is the same as the slope or rate).

Some problems will ask for that k value (which is called the constant of variation or constant of proportionality - it’s like a slope!); others will just give you 3 out of the 4 values for x and y and you can simply set up a ratio to find the other value. I’m thinking the k comes from the word "constant" in another language.

(I’m assuming in these examples that direct variation is linear; sometime